The main difference between Spelljammer and Spelljammer: Shadows of the Spider Moon is scope. Spider Moon is one sphere, isolated from the rest of the Spelljammer universe. The mini-game did not have the space to go into celestial mechanics and travel from sphere to sphere. So in order to make this document complete, I had to find a way to update the idea of crystal shells and the phlogiston (or the flow). The best resource for updating Spelljammer celestial mechanic is the D&D Manual of the Planes.
Now, before I go any further, here are some basic definitions of key Spelljammer and planar terminology when it comes to celestial mechanics.
Coexistent - If a link between two planes can be created at any point, the two planes are coexistent.
Coterminous - Planes that link together at specific points are coterminous.
Crystal Shell - A sphere's system is bound by a crystal shell or crystal sphere. The inside of the crystal shell is the vacuum of wildspace, while outside the shell is the phlogiston. A crystal shell is composed of an unbreakable, dark, unidentifiable material of unknown origin. Each crystal shell may encompass several worlds, which are each, their own Material Plane. The surface of a crystal shell is neither part of wildspace or the phlogiston. And while crystal shells can be thought of as being Transitive Planes, to the phlogiston, for the sake of reason each individual crystal shell should be defined as a Demiplane unto itself.
Demiplanes - A catchall category that covers all extradimensional spaces that function like planes but have measurable size and limited access. Crystal shells can be thought of as demiplanes.
Material Plane, the - The Material Plane is defined as being a traditional fantasy world where the basic laws of physics work like the players expect them to. Thus, each planet is said to be a material plane unto itself. Those living on a material plane world often use the term Prime Material Plane when referring to the concept of the Material Plane. A material plane can be different for each world, thus allowing for different planar cosmologies. A typical Material Plane has the planar traits listed on page 41 of the D&D Manual of the Planes.
Phlogiston, the - The phlogiston or the flow is often referred to as a rainbow ocean of flammable ether. It is also commonly referred to as a multicolored sea, upon which 'float' the various systems within their crystal shells. It has varying thickness in space and forms dense rivers between the spheres and any planet-sized objects. The term phlogiston is applied equally to both the multicolored medium and to the entire region surrounding the crystal spheres. The phlogiston is its own plane, which I will sometimes refer to as the Plane of Incandescence. The phlogiston is a Transitive Plane.
Sphere - Sphere is the common term used when referring to crystal shells and the celestial bodies within (i.e. Kulan's sphere). Many famous crystal shells have alternate names, which are easier to use (i.e. Realmspace, Greyspace, and Krynnspace). And while the inhabitants of Kulan often refer to their sphere as Kulanspace, very few beyond that world call it that. In fact, if you asked someone from Realmspace where Kulanspace was they wouldn't know (i.e. "What sphere is that?").
Transitive Planes - A mixed bag of planes that are grouped together by a common use: getting from one place to another. The phlogiston and wildspace are both transitive planes. Crystal shells are, theoretically, transitive planes that allow travel to and from wildspace and the phlogiston.
Wildspace - Wildspace is an airless void that exists within each crystal sphere. Interplanetary journeys around a solar system take place within wildspace. For the most part, wildspace is like normal real life space. Wildspace has many names such as space, arcane space and the airless void. Students of planar cosmology often refer to wildspace as the Infinite Planes of the Starry Void. And while there are as many 'wildspaces' as there are crystal shells they are all strangely connected and are thought of as one plane with billions of unique sub-planes. The best way to look at it is that wildspace is similar to a myriad planes cosmology within the bounds of the D&D Cosmology. Wildspace is a Transitive Plane.
Every spelljammer system is enclosed by what is known as a crystal shell - a hollow, spherical demiplane made out of the very building blocks of the universe. Most believe this material is some sort of indestructible ceramic compound, which has defied all testing by many alchemists who insist on knowing instead of just accepting.
A crystal shell defies the logic of physics, as it is known on the Material Plane. The shells are a mystery that could takes millions of years to unravel. Priests often speak of the will of the gods when they debate the issue of crystal shells and how they could possibly exist.
What is known is that each crystal shell is unique and has a measurable size. A sphere's crystal shell is usually at least twice the size, in radius, than the orbital radius of the outermost celestial body in the sphere. Of course, there are exceptions to this rule but only the most skilled sage would know which shells vary from the norm.
For more details on crystal shells, read the corresponding section in Concordance of Arcane Space (pg. 9).
Crystal shells are coterminous with both the phlogiston and wildspace. Crystal shells are considered separate planes from all other planes. Thus, one cannot go from the surface of a crystal shell to the Ethereal Plane or the Astral Plane, for example. It is this restriction that prompts planar sages to classify crystal shells as demiplanes.
Note that a standard crystal shell has no means to allow life to survive upon it. There isn't any gravity or atmosphere. Characters will need a magical way to survive and move on a crystal shell (i.e. Telekinetic Sphere). Unique or variant shells might have an atmosphere clinging to the inside of the shell or have elemental pockets embedded in them. This depends on the individual campaign model of the DM.
A typical crystal shell has the following planar traits:
While crystal shells are affected by certain spells to allow passage to and from the phlogiston, they almost never have portals to other planes. You could allow a crystal shell to have one or two permanent magical gates to the Inner or Outer Planes but it will depend on each Dungeon Master's campaign model. If they exist, such gates should be rare and hard to activate. A unique crystal shell with a civilization on the inside of the shell would be a good choice for links to other planes.
Crystal shells almost never have any form of native life. If a crystal shell has life it most likely will be sentient. A crystal shell could, instead of having planets within it, have a civilization on the inside of the shell with the sphere's star in the center of the shell. Such systems are very rare in the universe.
Encounters: Most encounters near or on a crystal shell will be with other adventurers trying to pass through the shell into the phlogiston. However, there are very few places where characters won't encounter something. Thus, characters could easily encounter vacuum-based creatures on a crystal shell.
Other common encounters near or on crystal shells are the ruined hulks of spelljammers whose captains misjudged the distance to the edge of the shell. These ruined hulks are often haunted by the now undead crew, which could be made up of ghouls, zombies, wraiths, and/or ghosts.
Outsiders and Elementals: Another rare encounter on crystal shells is with Outsiders and/or Elementals. These beings are never native to a shell but could be encountered there if they were somehow summoned and trapped there. Elementals don't need air to live and are the most encountered planar creature on or near crystal shells.
In some cosmologies there is the Plane of Vacuum, which, for the most part, is exactly like wildspace. Any creature native to such a plane could easily be adapted to living on a crystal shell and characters might be surprised to encounter entire nations of such creatures on a crystal shell's surface.
On a typical crystal shell it is next to impossible to move with any sort of control. A character could theoretically pull him or her self along with his or her hands on the inside or outside of the shell. Such a feat would be next to impossible without proper zero-gravity training.
Combat on a Crystal Shell: Combat on a crystal shell cannot take place unless the shell has variant gravity and/or atmosphere traits. A crystal shell with standard gravity would mean that combat would be similar to being on the Material Plane. This, of course, is up to each individual DM to decide.
Most crystal shells are featureless. They are totally pitch black. A typical crystal shell hasn't any handholds or rough edges and is smooth to the touch. However, a unique crystal shell with strange features is possible. See under Features of the Infinite Planes of the Starry Void, for other possibilities of how a unique crystal shell might be formed.
Alternate Shapes: Crystal shells are round 99% of the time but there are a few shells that defy this pattern and appear as cubes, cylinders or even stranger irregular shapes. These strange crystal shells are disturbing to even the strongest willed stellar sailors.
Material Plane sages often describe the phlogiston as a rainbow ocean or a multicolored ether sea, which to planar sages is a misnomer. The Plane of Incandescence is infinite in size and visitors can see in every direction, regardless of orientation. However, the plane appears to have an up and down to it despite being three-dimensional and having a variant gravity, which is frightening to a novice traveler. Of all the planes of existence, the phlogiston is the most unlike any other.
The phlogiston is best described as a great, endless void of rainbow-colored ether, both above and below with varying levels of thickness to the plane's ether. These thick regions of ether form dense tubes or 'rivers' between the crystal shells and any object of, at least, planetary size.
The ether of the flow is thicker below than above when one enters the plane and this is how natives of the Material Plane came to refer to the flow as a multicolored ocean. In reality, the plane's ether is simply not as dense in the upper half of the plane as the lower half. This gives the appearance of a thick, multicolored ether ocean below a thin, multicolored ether sky.
The other key features of the Plane of Incandescence are the millions of crystal shells that 'bob' in the ether of the flow. This too, as planar sages put it, is a misnomer. The crystal shells don't so much as bob as they do drift through the ether of the phlogiston. Crystal shells gravitate towards the ether of the plane and are almost always found where the ether is the thickest. This means that the crystal shells tend to drift somewhat parallel to each other through the central part of the plane, near the ether rivers.
Of course, there are exceptions such as the sphere of a world called Athas which isn't linked to an ether river and is, therefore, next to impossible to get to, even for those who know where to look. And while this phenomenon isn't common it isn't unique to that sphere. In fact, it isn't even that rare, as there are billions of crystal shells drifting through the ether-filled void of the phlogiston. Thus, crystal shells can be found anywhere on the plane at any time as the drift continuously.
Planar sages point to the Infernal Battlefield of Acheron as an example of how the drifting of the crystal shells works within the Plane of Incandescence. On Acheron, colossal, continent-sized iron cubes float through an airy void. The main difference between the two planes is that, on the phlogiston, the ether of the plane keeps the crystal shells from colliding. For when two shells drift together the ether becomes thicker between them providing a natural barrier to prevent disaster. The shells then drift apart each going in the opposite direction of their original heading. It is this random drifting which forces crystal shells into any and every part of the phlogiston.
The phlogiston is coterminous to both the crystal shells and wildspace but not to the Material Plane. And does not touch the Material Plane. Thus, one has to move from the phlogiston through the crystal shell to wildspace first then to the Material Plane on a spelljammer. The phlogiston is coexistent with the Ethereal Plane but does not touch the Plane of Shadow. The phlogiston doesn't have an atmosphere of any kind and is a perfect vacuum.
The phlogiston has the following planar traits:
Two main links to other planes exist on the phlogiston - the crystal shells and the ether rivers. The crystal shells link directly to wildspace through the use of arcane or divine spells that allow a character to create a portal, teleport or even phase through the shell. And while it can be said that the ether rivers don't link physically to another plane beyond the phlogiston, it is important to remember that each individual shell is its own demiplane unto itself. Thus, the ether rivers of the phlogiston are like extremely thick conduits through the rainbow void.
Because the phlogiston is coexistent with the ethereal, it is possible to shift to that plane through the use of arcane & divine magic or psionics. This means that a spell such as Ethereal Jaunt and Etherealness could allow a character to escape the phlogiston if their air supply becomes tainted. For while there isn't any oxygen on the phlogiston, there isn't any such restriction on the ethereal. Note that a journey from the phlogiston into the ethereal and then on to wildspace would be a very long journey unless the character happens to be near a crystal shell. There aren't any benefits to following the path of an ether river while ethereal (you can see into the phlogiston from the ethereal just as with the Material Plane). Time and movement are normal.
While the phlogiston isn't the most hospitable place for living things that require oxygen to survive, it isn't a lifeless void. In fact, the phlogiston, like wildspace, is teeming with a vast array of unique lifeforms beyond the frequent travelers simply passing through from one sphere to another.
Many beasts, both magical and mundane, have adapted to the vacuum of the flow. Creatures such as flow sharks and stingrays are common; as are flow barnacles (and the rarer infernal barnacles) and the shark-like scavvers. Another large beast that is only found on the phlogiston is the delphinid. These strange fish-shaped creatures are fairly harmless and love to 'swim' through the flow along passing spelljammers. Other, rarer, beasts include such things as puffers, kindori (space whales), the spaceworm and krajen. Adult krajen, or space squids, are the bane of the space lanes. Spelljamming crewmen fear for their lives at the mere thought of an adult krajen being nearby.
Many other creatures may be encountered in the flow but usually they aren't native to the plane. The allura, bionoids, graeae, monitors, plasmoids, silatics, star selkies and survivors have all been encountered in the phlogiston.
However, there are a few higher order lifeforms living on the Plane of Incandescence. The greatest of these are the radiant dragons and the sarphardin. Of course, these dragons are also encountered in wildspace but many planar sages believe the radiant dragons were originally from the phlogiston. The sarphardin is more often encountered in wildspace but is just as home on the phlogiston as well. Another sentient life form that is native to the plane is the flow ixitxachitl. These relatives of the aquatic ixitxachitl on the Material Plane originally developed on the Plane of Incandescence but can now also be encountered in wildspace as well. It is said that there are vampiric flow ixitxachitl that often can be found leading the lesser flow ixitxachitl. Spacefarer's often refer to ixitxachitl as space streakers.
One other lifeform is native to the phlogiston - flowfiends. These malevolent Outsiders are evil, sentient beings that have been transformed by an evil entity called the Great Father. Once transformed, the flowfiend loses all knowledge of its former life and becomes completely genderless. They 'swim' through the flow looking for food or other victims to convert, as this is the only way to add to their numbers. Some sages speculate that the Great Father created the flowfiends to conquer wildspace and Material Plane.
Beyond natural life, almost any form of undead could be encountered on the phlogiston from undead beholders to shadows and wraiths. Ghosts are a real menace due to the Ethereal Plane's coexistent nature to the Plane of Incandescence. Worse still are the ghost ships of those unfortunate enough to have died on the plane due to suffocation or starvation. Of course, the flow has its own undead menaces - the ancient mariner and the ephemeral. An ancient mariner is the undead spirit of a member of a long-lost race that once sailed the phlogiston. While, ephemerals are believed to be the spirits of individuals who have died in the phlogiston that look like dusty-gray humanoids.
Who or what your characters encounter on the phlogiston is only limited by ones imagination. Below are some D&D Monster Manual II creatures that could easily be adapted to or encountered on the flow.
|Banshee||Fihyr, Great||Shadow Spider|
|Chaos Roc||Jahi||Spell Weaver|
|Dire Hawk||Legendary Eagle||Thri-Kreen (sj race)|
|Elemental, Air Weird||Legendary Shark||Windghost|
|Ether Scarab||Leviathan||Yak Folk (sj race)|
|Ethereal Slayer||Morkoth (native)||- Titanic|
|Famine Ghoul||Neogi (spelljammer race)||- Warbeast|
Travel on the phlogiston is usually accomplished by visitors on spelljamming vessels. Rarely, does a visitor ride through the flow on the back of a kindori, for example. However, those creatures and intelligent races native to the plane usually have a means to travel the plane safely. Regardless of the mode of transportation, all travelers on the phlogiston use the ether rivers to travel from place to place.
Travelers have discovered, over the ages, that the greater the density of the ether rivers the faster time and spelljammers move. Since the difference in time is minimal in the rivers of the phlogiston, they are the fastest way to travel the spheres. Spelljammers can move though the upper half of the plane just as they can through the lower, denser half. It's simple way too slow for longer journeys without the aid of the ether rivers. Note that natives of the plane never have to worry about an increase in time while within the ether rivers of the flow.
As for movement while on a solid object, the planes Objective Directional Gravity means that up and down are relative to that object you are standing on. Therefore, a character can literally walk on either side of a spelljamming vessel, without worrying about failing off. Long-time spelljamming races have perfected the art of creating spelljammers that take advantage of this fact. This gravity effect also means that anything that escapes the gravity well of a spelljammer or other large object will float away from that object into the void of the flow until it comes in contact with another solid object.
Remember that the crystal shells exert no gravity upon objects or people. You cannot stand on a crystal shell but you can push off one in order to float away from it. Note that a single character of any size cannot alter the trajectory of a sphere by pushing off it, not even if that character is of colossal size. This goes for Avatars as well. (You know someone's going to ask that one.)
Something in the nature of the plane and the crystal shells always forces those entering the plane to appear in the theoretical middle of the phlogiston, as they leave a crystal shell. In other words, if a spelljammer attempts to leave a particular sphere, say, at the top of the shell then it will appear on the other side of the shell at this theoretical middle of the flow, as the center of the plane is evident for that sphere. Confused yet? Why this happens is a mystery indeed. Some planar sages suggest it is part of the universe's design or that the magic needed to pass through the sphere causes this. Of course, there is some deviation to this rule but for the most part a spelljamming vessel will appear within 10d100 miles of this theoretical middle of the plane.
Phlogiston Combat: See Leroy Van Camp III's excellent 3e Ship Construction and Combat Rules at Spelljammer: Beyond the Moons for how to run ship-to-ship combat on the phlogiston. I will probably add more details on person-to-person combat while floating in the rainbowvoid, during the second pass of this document.
The Plane of Incandescence isn't known for its sights but there are few places worth mentioning. Some of these locations and phenomenon are considered little more than rumors by skeptics and nay-sayers.
Astromundi Cluster: This fabled sphere, also referred to as the Shattered Sphere and Clusterspace, is said not contain any planets but only countless asteroids orbiting endlessly around the sphere's sun. More startling than this is that it is said that it is inhabited. Can you find this lone crystal sphere drifting through the Phlogiston? Can you find it and more importantly, can you live long enough to escape it?
Destroyed Crystal Shells: This is something that was never meant to happen. A Crystal Shell that has been shattered, allowing the ether and radiance of the phlogiston to mix with the blackness of wildspace. Such a destroyed sphere would be hard to miss as the countless, relentless undead of the sphere's dead worlds come screaming forth into the flow seeking to undo life wherever they find it.
Massive ether tornadoes rip across the inner bowels of the shattered sphere. The sphere's collapsed sun sucking in the ether of the flow, as a radiant black hole - beautiful and deadly. The planets broken and lifeless - massive asteroids and meteors near the sphere's edge, some slipping into the depths of the collapsed sun, while others drift off into the rainbow void as oddities of a disaster not even the gods would dare speak of.
These are the legends told by the inhabitants of the phlogiston. Expand your mind and your campaign!
The Etherdeep: Spelljamming sailors whisper of a tale told in the ports of call from one end of spheres to the other. They whisper of a place deep beneath the Ether rivers of the flow called the Etherdeep. Is said that if you take your spelljammer deep enough the ether becomes so thick in places that time speeds up so much that you go backwards in time rather than forward. Spelljamming captains with too much bravado have been lost in time in this place or so the story goes.
And all manners of strange creatures are said to exist in the etherdeep. Flow morkoth, kopru and worse. It is said that if you travel far enough you come out on the other side of the plane in some bizarre alternate reality where beholders and the neogi rule. Others say that on the other side of etherdeep are the home spheres of the arcane. Finding out could be a death sentence, as the etherdeep is said to be able to strip away years off your life.
Ether Shift: Some of the oldest elven captains talk of a place on the plane where everything reverses called Ether Shift. The ether rivers of the lower half twist upward into the ether sky, which quickly becomes clogged with the dense ether rivers while the lower half opens into a thinner ether sky, giving the perspective of being upside down to those use to the natural order of the plane - relative to the known spheres. Of course, most people think these old elven captains might want to consider drinking less elven wine.
Flowfalls: Some travelers have reported seeing huge multicolored waterfalls that seem to flow up, relative to the observer, into the upper half of the plane stretching into the distance and out of sight. It is also rumored that a single solitary sphere drifts within the flowfalls near the edge of the falls, balanced precariously on the edge.
The Lost Dead God: Some spelljamming captains swear they have seen the massive remains of what is obviously a dead god, floating through the phlogiston. Sages believe that, if it exists, the god was brought to the Phlogiston by its faithful followers in hopes of reviving the dead god. These followers are gone now but the lost dead god remains. Were these captains blinded by the radiance of the flow or does this lost deity exist? And they swear they saw the god stirring.
Radiant Triangle: These three spheres are no legend. They are the spheres of Realmspace, Krynnspace, and Greyspace. They form a stable triangle in the chaotic drift of the Phlogiston. Travel is possible in both directions between Realmspace and Greyspace, and between Greyspace and Krynnspace. However, an ether river does not connect Realmspace and Krynnspace, so while a direct trip from one to the other is possible, it is very slow.
Sphere of the Spider Moon: The home sphere of Andy Collins' Spelljammer: Shadow of the Spider Moon. Buy the magazine buddy!
The Infinite Planes of the Starry Void. Wildspace. The Dark Airless Void. All these names refer to the plane with billions of possibilities. For every crystal shell there is a wildspace. The dark void which separates the worlds of the Material Plane within a sphere. Wildspace is often referred to as Arcane Space, which isn't exactly right. For while wildspace is a part of Arcane Space it isn't the only part. Arcane Space is the crystal shells and the phlogiston, as well as wildspace. However, most sages believe that wildspace is the key part of Arcane Space, as it is where one has access to the countless Material Plane worlds.
Note that wildspace isn't exactly one plane but a multitude of planes that are linked together by their common features and functionality. This is how planar sages have come to call wildspace the Infinite Planes of the Starry Void. For each crystal shell has its own wildspace, which is separate from every other wildspace across the interstellar cosmos. The 'wildspaces' of the universe drift through the vastness of the phlogiston protected by their crystal shells. It is a mind-blowing concept that all these individual wildspaces are connected when they never physically touch. But they are because they all share the same planar traits (for the most part).
All of the celestial bodies within a crystal shell float in the airless void that is wildspace. Of course, planar sages again point out that using the word 'float' doesn't really describe how these bodies move. A planar sage uses the words cycle or orbit to describe the movement of the celestial bodies. Of course, each wildspace, while similar, is unique. Note that not all celestial bodies move in this cyclic fashion although most of them do.
Wildspace is considered coterminous with the Material Plane, the crystal shells and the phlogiston. Wildspace is also coexistent with the Ethereal Plane and the Plane of Shadow. Why wildspace touches the Plane of Shadow, while the phlogiston doesn't is a mystery to planar sages. Perhaps wildspaces' closer nature to the Material Plane caused it to naturally become coexistent with the Plane of Shadow. No one knows. Wildspace doesn't have an atmosphere of any kind and is a perfect vacuum.
The typical wildspace of a single sphere has the following planar traits:
Also, many divine spells such as Call Lightning don't work in the depths of wildspace because of the spell's link to the natural world. It is the choice of each DM to decide which spells he or she wishes to restrict in the cold vacuum of wildspace.
Note that the spell Imprisonment doesn't have any effect in wildspace, although it functions normally on any celestial body (planet, asteroid, etc.).
Wildspace links to millions of Material Plane worlds, as well as the crystal shells. And while the phlogiston is coterminous with wildspace, in order to travel from wildspace to the flow one must cross either the barrier of the crystal shells or take a trip through the ethereal. In other words, one could say that the crystal shell is the link between wildspace and the phlogiston. This is the simplest explanation and most travelers don't wrack their brain trying to under stand how it all fits together - it simply is.
Links to other planes are possible in wildspace. Many spheres have links to the one of the elemental planes or the Inner Planes. Most often these links are actually on a Material Plane world. However, sometimes a direct link from wildspace to one of the elemental planes forms causing elemental material to spill out into the depths of wildspace. Such an elemental portal is rare. Even a portal to the Positive or Negative Energy Planes could form but are very rare. Spheres with energy portals are either teeming with life across the entire sphere or are dark, haunted places filled with the undead.
The Inner Planes aren't the only planes that can be linked with wildspace. One of the deities of the Outer Plane might have a particular interest in a sphere and create a portal from its home plane to wildspace. However, a deity rarely creates such a portal permanently.
The Ethereal Plane and the Plane of Shadow are both coexistent with wildspace but rarely does a permanent portal form between these planes and wildspace. Ethereal Jaunt and Shadow Walk are good ways to temporarily escape a bad situation such as a fouled atmosphere or deadly monster (as long as that monster can't follow you).
Many of the animals, beasts and magical beasts that exist in the phlogiston also live in wildspace. Scavvers, puffers, kindori, spaceworms, and krajen are just as home in the Infinite Planes of the Starry Void as they are on the phlogiston. However, the infinite nature of wildspace has spawned numerous creature not normally found on the phlogiston - buzzjewels, comet steeds, firebirds, giant space hamsters, lhee, q'nidar, skullbirds, space owls, space swine, zards and zurchins. And those are just a few of them.
Wildspace inhabitants can range from colossal sun & moon dragons to the minute feesu. And new life forms are being discovered every day by xeno-biologists. Beware the deadly astereater, a large beholder-like aberration that looks like a small asteroid. It is said to be good luck amongst spacers to spot the beautiful and peaceful al'haq'ah galloping silently across the starry void. No spacer is ever happy when the dark blue sluk, or wildspace seaweed, gets caught in ones rigging or worse yet, tries to engulf you in order to devour your precious magic.
Yes, anything may be out there in the Infinite Planes of the Starry Void.
(Make sure you visit Shattered Fractine's Monster's of the Void for dozens of Spelljammer creatures just ready to give your characters fits. Also make sure you visit Spelljammer: Beyond the Moons' Monsters of Wildspace for the latest official Spelljammer conversions for 3rd Edition, as well as some 2nd Edition monsters not found anywhere else.)
A conventional interplanetary journey around a particular sphere's solar system takes place through wildspace. It is the first obstacle that must be dealt with by anyone wanting to travel through space. In most cases, this journey takes place on a spelljamming vessel of some sort. However, there are other options including the extended use of magical spells or psionics. However, such alternate journeys are long and hard on a person physically and mentally. It is for this reason that spelljammers were designed.
As for movement while on a solid object, the planes Objective Directional Gravity means that up and down are relative to that object you are standing on. Therefore, a character can literally walk on either side of a spelljamming vessel, without worrying about failing off. This gravity effect also means that anything that escapes the gravity well of a spelljammer or other large object will float away from that object into wildspace until it comes in contact with another solid object.
Wildspace Combat: See Leroy Van Camp III's excellent 3e Ship Construction and Combat Rules at Spelljammer: Beyond the Moons for how to run ship-to-ship combat on wildspace. I will probably add more details on person-to-person combat while floating in the starry void, during the second pass of this document.
Since each wildspace is different there really aren't a set of defining features for wildspace, as a whole other than it's a black, star-filled void. And that's not really a good choice of words as there aren't any real stars in wildspace beyond the system's own star (also called a fire body or fire world). So why do you see stars from the Material Plane or from the deck of a Spelljammer coming up out into space? That is a good question.
Some believe that what we perceive as stars, are really the billions of other crystal shells' stars. But how can you see those shells' stars though the shells and the phlogiston? Another good question. The answer that planar sages have come up with is that a system's crystal shell isn't visible from such a distance or, in other words, that the shell is invisible when not viewed up close. Startling thought, isn't it?
Of course, some crystal shells when view up close, reveal different options. Some shells have constellations actually etched into them, which glow bright enough to see from anywhere in wildspace. Others have round holes that allow the radiance of the phlogiston to spill into wildspace, which gives the appearance of stars. Of course, this doesn't explain how one sees stars in those systems without such distinguishing characteristic.
Elemental/Energy Traits: It is possible that a particular sphere's wildspace might not only have portals to one of the Inner Planes but could also have an elemental or energy trait associated with it. Such a trait might affect the type of worlds the sphere has or wildspace could simply be saturated with the element or energy making the sphere strange indeed. Imagine a sphere with its wildspace saturated with abnormally large amounts of water or fire. Or where thousands of elemental earth asteroids dominate wildspace. An energy dominant sphere would be a strange place indeed and possibly lethal as well.
Elementals and genies or stranger creatures, for the energy traits, would dominate such spheres. Plus, changing wildspace's traits in such a manner might also mean that the planes magic traits would be altered as well. The skies the limit, be inventive.
Ports of Call: Something that is the same across the known spheres are those places where spacers call home and mingle. The Rock of Bral is definitely the most famous port of call. Of course, everyone believes that the Rock of Bral is in his or her home sphere or in a nearby sphere. And maybe they're right. Could Bral exist in many spheres at once? No one knows and the residents of Bral scoff at such questions. Maybe your character can learn the truth.
Regardless, Bral isn't the only port of call in the known spheres. When traveling through the sphere known as Hyrkulspace one should look for an asteroid city called Hestia. This port of call exists within the sphere's asteroid belt and is known for its unique services and entertainment.
Other interesting locations to visit include Kame'ban, an isolated village built on the back of a gammaroid; Ander - the Hollow Garden, a settlement in a hollow asteroid; Jumble, a strange city that has multiple gravity planes across its asteroids surface; Miraburg, a forest covered asteroid in the dense asteroid belt known as the Grinder in Greyspace; Leasanar, an abandoned dwarven citadel. Caution is advised in setting down in just any community, however. Some of these communities might not be seeking visitors. You have been warned. (All of this paragraph's locations have a write-up here on Spelljammer: Beyond the Moons.)