For decades D&D had the Great Wheel Cosmology that during 2E was used to connect all of the D&D worlds mostly with the Planescape Setting and the Spelljammer setting to a lesser extent. Generally I do not focus on the outer planes that much except you have the Abyss for demons, the Nine Hells etc for devils. This thread s about how I would design a basic cosmology of your own. The 3.0 Manual of the Planes also discusses how to do this From Page 201. One can even buy that book here on PDF.
http://www.rpgnow.com/product/25109/Manual-of-the-Planes-3e?it=1
In my own games I may use the great wheel or I may use something else. When designing your own cosmology one needs to consider several things.
1. Where do outsiders come from?
2. Where do the gods live- if they even exist?
3. What influence do the planes play on your world.
The Greet Wheel may have gone overboard here and there with planes for various energy types and a home plane for every alignment. Early D&D had this as the Elric of Melnibone novels were an influence on D&D and the powers of law and chaos were cosmic entities.
This thread is about a nice and simple cosmology stripped down and focusing on the 3 questions I posted above. I will also focus on good vs evil law vs chaos not so much. So all things considered we need a home for outsiders and to make this easy I will just look at good and evil.
The Plane of Darkness
The Plane of Light
Nice and simple all fiends come from the plane of darkness, all celestials come from the plane of light. There would be no blood war in this scenario, deities of this world would likely be a creator type deity perhaps their wife or husband and children. An evil deity of course would oppose them. It doesn’t have to be this way of course just keeping it simple.
Now this leaves things like elementals. One could have 4 building blocks for elemental planes and one could even include para and quasi elemental planes as well where the planes over lap. The focus is on simple though so I will lump them all together. I will steal the elemental chaos from 4E.
Elemental Chaos.
In essence I have scaled most of the D&D outer planes down to three. D&D has usually had a transitive plane to get from A to B usually the Astral or Ethereal plane. One could mash both of those planes into one however. I will call the plane the Transitive Mists.
Transitive Mists.
This gives us 4 planes now. Now one has to think about what creatures exist in the traditional D&D universe and where they come from. It would be obvious where demons, devils, celestials and elementals come from but what about Githyanki, Slaadi, Modrons etc. Well until they turn up in an adventure they may as well not exist in your campaign. They exist “off camera”. If need be one could always add limob as a plane in the transitive mists. Perhaps you want to use the plane of shadow or the shadow fell. That is easy enough to add it exists between the plane of light and darkness.
Plane of Shadow
If one had to draw a diagram of this multiverse the prime material plane would be the core and it would be surrounded by the elemental chaos. Beyond this would be the planes of light, shadow and darkness and all of the planes would be surrounded by the Transitive Mists. Quasi elemental planes would be where the elemental chaos overlaps with the plane of light or darkness, the paralemental planes would be where the elements collide in the elemental chaos, Other planes would float in the transitive mists if required.
And that’s about it. Ok my cosmology may be a silly one but I dreamt it up in about 2 minutes and with 5 planes I can cover most of the D&D multiverse and have room to add in extra planes if required. As I said a very basic idea and one could easily expand it if required or break the elemental chaos into air, earth, fire, water etc.
I have enuogh of the relevent books to follow that Artifact.
4e didn't do away with ethereal-based spells; it just changed any use of the word 'ethereal' in a spell discription to 'insubstantial'. 4e's take on the cosmos/planes did get rid of the ethereal plane.
I like both takes, for different reasons. If I choose to make a campaign setting were alignment really matters (an idea I'm toying with) the great wheel will be used, with a plane for each alignment. If I don't do that, I'll stick to planes above (astral + good), planes below (elemental + evil) and make the prime material (world +shadowfell + feywild) as neutral.
I do like having a feywild and shadowfell. A lot. They are awesome to use, IMO. But I like them being unaligned, like the 'real' world AKA material or Prime Material.
I also like the Far Realm. That'll get used too, no matter what.
My homebrew setting has a very simple cosmology.
The planes:
- Paradise
- The material world
- The spirit world
- The netherworld
The Material World
The Material World is simple enough, it's the Great Wheel and World Axis equivalent of the Prime Material plane only that there is just one world in it, the world my setting takes place on; I refer to it as Tenesia, but that's actually just the name of the most notable continent on that world.
The Spirit World
The Spirit World is basically the Border Ethereal plane for the Great Wheel.
Paradise
Paradise is the Heaven of my setting; it is the home of the good deities and the Angels/Blessed Ones.
The Netherworld
The Netherworld is the Hell of my setting; it is the home of the evil deities and the Devils.
Angels, Devils, Demons, and the Blessed Ones
In my setting, Demons, Devils, and Angels aren't separate groups of creatures who originate on different planes. Instead, D&D's Angels, Devils, Demons, Slaadi, & Yugoloths (who I will call outsiders as a shorthand) can all be good, evil, lawful, chaotic, or neutral as they please, and they serve a deity of their choosing. Each religion sees the outsiders that serve their god/goddess as Angels. The outsiders that serve other gods/goddesses are called either Devils or Blessed Ones depending on the relationship between the two deities.
For example: In general, followers of a good deity refer to the outsiders that serve their deity as Angels, the outsiders that serve other good deities as Blessed Ones, and the outsiders that serve evil deities as Devils.
Demons are outsiders who refuse to serve a deity, and Fallen Angels are outsiders who turn evil or leave the service of the deities to become masterless creatures.
MechaPilot wrote:
Yeah the Great Wheel and World Axis (and even the World Tree) cosmologies often have almost the same exact planes, they're just visualized in different ways, with different emphasis placed on various planes. Since the planes in effect co-exist in the same physical location just on different slices (planes) of reality all most cosmologies do is try to find a way to visualize them and make links between them.
Look at Krynn, it's cosmology is very simple and while they don't have access to the full set of planes, what they have access to is a subset of the World Axis and Great Wheels. Athas is similar in that it's cut off from most of the planes but not quite entirely. So while these worlds can exist within an overarching Great Wheel or World Axis cosmology the inahbitants of those worlds may not view the cosmology that way since they're not aware of all aspects of it. Krynn calls Tiamat's domain in the first layer of Hell the Abyss, which for a non-Krynn native might be confusing if they're aware of The Abyss and the Nine Hells, and that Takhisis is Tiamat.
Outside of some spells and items, the rules are pretty cosmologically neutral and can hold up when you create a new or alter an existing cosmology to fit your campaign world. You just have to keep in mind how it does impact spells and items that reference other planes, and possibly find new homes/backstories for certain creatures (or exclude them entirely).
Some examples:
No Elemental Chaos/Planes: elementals are purely conjured constructs with no sentience. Genies just have elemental affinities and tend to inhabit sections of the world strong with that element: efreet in volcanoes, marid in the oceans, djinn on mountain tops of solid cloud castles, dao in caves.
No Nine Hells/Abyss: No blood war, demons and devils may reside in the same plane with a different heirarchy. Maybe demons are beneath devils who see themselves as the rulers of some plane of evil or netherworld where the unholy are punished.
No Ethereal: This one has the most impact on spells and items likely to be used by most adventurers. How do ghosts work? Does ehthereal statuses just translate to insubstantial but still part of the Prime? Do things like Secret Chest instead just reside in some sort of localized, temporary demiplane/pocket dimension like a Bag of Holding's interior?
No Astral: How do entities travel between the outer planes (realms of the gods)? Is there another method that connects the Material to the Outer? Is there anything at all between the planes?
The names of planes can even change. In various Asian-influenced cosmologies the Astral could be called the Void and tied to the Elemental Planes but still being the transitive space between the planes, rather than a plane in and of itself. They also point out that the Feywild can also be known by names like Faerie, or merged with Arcadia if you want to rename/remove that Outer Plane. The Shadowfell is just a renamed Plane of Shadow.
Cosmologies are more about fleshing out a campaign setting than they are about deciding rules mechanics. The choice in cosmology helps to flavor a campaign setting. The layout, naming, and features given to the various features of the cosmology can and should reflect the ideals, outlooks, and morals of the campaign world inhabitants.
Note: Same post in two threads since they're related in theme and this applies well to both.
I'm kicking around a linear World Tree cosmos. Much inspiration from Larry Niven's The Integral Trees for travelling along the tree. But I don't want the tree's roots to be in the Hells or the Abyss; that would kill off the tree! Still thinking ... 
I liked the Astral Sea a lot. I think I'm most likely to use basically the Great Wheel, but with the Astral Sea instead of the Astral Plane.
They serve similar enough purposes that you can just replace one with the other.
The cosmology of Erithor (my homebrew setting) takes a lot from The World Axis of 4e, along with elements I've had in my setting since I first wrote about it in high school. The planes are:
The Crystal Sphere -- This is the boundry of Creation. Inside is everything that was created at the dawn of time by The Nameless One. Outside it is The Far Realm, where the Primordial dwells. Normal magic cannot pierce this sphere--you have to physcially travel to one of the places where the sphere has been cracked to pass through. The Crystal Sphere is mindbogglingly huge but it is, in fact, bounded (that is the entire purpose of having a boundry).
The Far Realm -- "outside" the crystal sphere is The Far Realm, an insane, maddening realm of all the possibilites that The Nameless One rejected for one reason or another when he was building Creation. The Primordial, an ancient sentience accidentally created by The Nameless One as he named the first gods, dwells here. The Primordial is generally depicted as a dragon made of red clouds in religious texts, but in truth it has no real form -- it was a mistake. It views the orderly Creation as a painful tumor in the face of infinite possibilities, as Creation includes all the possibilities The Nameless One chose to make "real." The fixed form of reality is an affront to The Primordial, and it would destroy all of creation were it not kept at bay by The Crystal Sphere. It has been trying for eons to break the sphere, and it has created a few cracks where it's influence can be felt: The Abyss, where demons dwell, and The Stars of Ill Omen, corrupted parts of The Astral Sea. Aberrations come from either The Far Realm itself, The Abyss, or The Stars of Ill Omen.
Inside the Crystal Sphere, the empty space is divided into The Astral Sea, The Elemental Tempest. In the center, forming the axis of ths cosmos, are The Three Worlds and The Twin Rivers.
The Astral Sea -- When The Nameless One first began creating, he made a clear, silent space where he could contemplate. The Astral Sea is that space. It is a place for ideas. It contains all the heavenly bodies, The Ten Thousand Wonders that make up the Middle World's night sky.
With the Astral sea is:
Heaven: The meeting place of The Gods, and the throne from which they rule. Heaven is not where they live, just where they gather. It forms the moon of Eirthor. Angels dwell here, serving as messangers and warriors for the Gods.
The Seven Hells: Created as prisons for demons after The First War, the Seven Hells were parts of the Ten Thousand Wonders that The Seven pulled closer to The Three Worlds to work on when they couldn't agree how best to torment the demons they had captured. When The Seven fell to evil, it was here that they and their followers (which became the Devils) were thrown by The Nine Heroes. The Seven Hells represent the planets in Erithor's solar system.
The Ten Thousand Wonders: Before The Nameless One began work on his most perfect creation, he experimented with various combinations of energy and matter. These experiments were left to shine in the night sky. There's probably far, far more than ten thousand of them--that's just the name they've gathered by poets over the centuries. This is where the homes of the gods are, but there's an aweful lot of space for other outsiders and creatures that would appear to be Aberrations according to the physical laws of The Middle World. The Wonders represent the other stars in Erithor's galaxy.
The Stars of Ill Omen: These are Wonders that have been corrupted by the Primordial thanks to cracks in The Crystal Sphere. They are sentient, but their motives are strange and difficult for mortals to comprehend. Some of them birth monsters to plague Creation, some of them work to corrupt and subvert, some seem friendly to mortals (but have a passive-agressive streak), and some are just dangerous the way forest fires and eathquakes are--impersonal dangers. The vast majority of Aberrations hail from these distant stars.
The Region of Dreams: A strange realm of thought and desire made manifest. Techically, it is part of The Astral Sea, but it works by very different rules. Sleeping minds form a connection to The Region of Dreams, pulling substance from the realm to create short-lived worlds. Most demiplane created by magic can be found here, and people can travel physcially to the realm using spells of etherealness. The Region of dreams serves as Creation's Ethereal Plane. The Region of Dreams forms the night sky of The Feywild.
The Elemental Tempest -- a churning mass of entropic breakdown, The Elemental Tempest is where matter and energy are broken down, to be recycled later. Unlike the more regimented Astral Sea, The Elemental Tempest doesn't have many distinct regions. Temporary islands of stability can be formed through sheer mental effort, and some, such as The City of Brass or vrious Githzerai monestaries, can remain stable for thousands of years. The Elemental Tempest is where elementals dwell, as well as the corrupted elementals known as demons.
The Abyss: The Abyss is a series of cracks in the Crystal Sphere, analogous to the Stars of Ill Omen in the Astral Sea. Elementals corrupted by The Pimordial dwell here. Many of the cracks were sealed over after The First War, and the demons were trapped within. Bahamut, The Platinum Dragon, was given the duty of guarding the seals to the Abyss. Still, every so often demons manage to make their way into the wider reality, and the Demon Lords are working to break the seals that keep them trapped.
The Three Worlds And The Twin Rivers: The center of reality is composed of The Three Worlds (Shadowfell, Middle World, and The Feywild) and the Twin Rivers of Time and Life. Once, The Three Worlds were one Perfect World, but a civil war among the gods smashed The Perfect World and it had to be rebuilt. The gods couldn't agree on how best to remake the world, so it was separated into three parts.
The Middle World: The most balanced of the Three Worlds, The Middle World is what would be considered "The Prime Material Plane." It sits equally distant between the Rivers of Time And Life, and so it has the most varied biomes. This is where you will find most of the mortal races. The sky of the Middle World is The Astral Sea, and the relatively fixed points of the Ten Thousand Wonders means that navigation by starlight is possible.
The Shadowfell: The Shadowfell is a dark, twisted world. It lies close to The River Of Time, and thus is where the spirits of the dead travel when they die. The Shadowfell has a bleakness to it, even during the day, and the sky of the Shadowfell is the ever-churning Elemental Tempest (meaning that it can be hard to navigate).
The Feywild: The Feywild is vibrant and colorful, filled with magic and long-lived fey creatures thanks to being so close to The River of Life. But it is an unstable place--the magic is wild and the inhabitants tend to be somewhat crazed. The sky of the Feywild is a twilight formed by The Region of Dreams, where stars formed by the dreams of men appear and vanish at random (which is why you must never, ever trust the night sky to guide you, and always keep to the paths).
The Rivers of Time and Life: These rivers flow into each other, and together they keep reality moving. The River of Time is the river of endings, entropy, and breaking things down. Mortal souls are drawn to the River when they die, to be washed clean of their former lives before they travel to the River of Life to be reborn. The River of Life is a vibrant, glowing river where mortal souls are released back into circulation to be born again.
I don't use this in my own games. I haven't defined any cosmology as I don't see the benefit of it. I do however say that scholars in the material plane have many different theories and include all past cosmologies within that model. I also note that scholars can spend an inordinate amount of time arguing over whether the elemental chaos is a spot where all of the elemental planes converge or if all of the elemental planes exist within the elemental chaos.
If I were to go with a super-simple model I'd probably base it off the World Axis with only 3 planes of existence, which would be:
- Elemental Chaos
- Astral Sea
- Material Plane
There's no "passage" from one plane to another. When using spells like plane shift no plane is easier to travel to then any other plane.
Within these planes we have "dominions" or "echoes". These are specific places within the plane they exist in.
- Elemental Chaos: Contains the following dominions: Abyss, Nine Hells, Plane of Fire, Plane of Earth, Plane of Air, Plane of Water, Limbo (the absense of all elements)
- Astral Sea: Each of the gods have their own dominion here.
- Material Plane has the following echoes: Feywild, Shadowfell, Ethereal Plane
Echoes are duplicates of the material plane but with a significant difference.
NOTE: It is easier to travel from an echo or dominion to the reality it resides within in that the level of the spell required to travel in and out of a dominion is of a lower level than Plane Shift. Exceptions to this are the Abyss, Nine Hells and Athas which are all planar black holes (easy to get into, very difficult/impossible to get out of).
As for the Far Realm in my homebrew campaign the Great Old Ones come from the universe before the current one and live in deep space (where they lie asleep for now). They transformed a few worlds in their image which is where all aberrations come from. These aberrations are now doing the bidding of the Great Old Ones who seek to remake the current universe in their image.
Great thread, I've enjoyed reading everyone's different take on this, it's been in the back of my mind to think about the cosmology of my own home brew setting, but doesn't really need to be concrete for a while. I use the idea that not much is known / there are many different theories for a lot of my world.
i really like the 'where do the gods live' question, seems so simple, but it's a really good starting point.
Neonflux wrote:
Our idea for our homebrew campaign (Endermor is the main continent. I...ashamedly forget the name of the actual planet/plane) is quite inclusive. We usually view the current "standard" cosmology, and since we started with 3.x, we do things like the great wheel, with a twist.
EVERY plane of existance is accessible. Every single one. So naturally things like the elemental planes and 16 outer planes (Abyss, Nine Hells, Carceri, etc) are available to travel to, if you can find a way. On top of that, we've had characters from Eberron make it here (and vice-versa when we did an Eberron adventure), we've had people from Massachusets and Kansas, stuff like that. The trick is, some of these other "parallel" material worlds are hard to find, requiring great magic (like a diety using Wish, basically) or a well-plotted star-map of sorts.
I've actually toyed with the idea that to reach these seperate universes, you must first enter the Far Realm, survive that, and find the correct portal. This idea struck me when I made my Arkham Horror character, who traveled to the "DnD" world after coming from Earth. He traveled to what is essentially the DnD equivalent of the Far Realm. And after gaining great power from Yog Sothoth, he wound up in our custom world. But one could wander aimlessly, go mad, get eaten by Shuggoths, or slip into nothingness if you're not careful, so that's why travel across these different universes is both rare and difficult, reserved for old hats (like my weird warlock character) or deities (his demi-god buddy from that realm who travels to meet with him occassionally, at the local Starbucks).
I've always seen the Astral Sea as sorta like outerspace, personally. And this always led to the idea that you could travel to different planes, or certainly find portals to them, when traveling in a spaceship (or astral ship or whatever). Who knows! Maybe you can also get to a place like Greyhawk, and then to Krynn, from our world by leaving the atmosphere and charting the proper course! Failure to do so however...
As for directly parallel planes, the Shadowfel exists as it does (or similar enough) in 4E, since it's a parallel plane and is the same size/space of the material world but with different rules and geography. We're not super big on Fey, so the Feywild is probably just a separate plane of existance, not a parallel one (it could be, though, it's just never come up). The Ethereal realm exists, sorta as a hazy bubble that encapsulates the material world (AND the Shadowfel, probably, hasn't come up yet, but I like to think it does).
This may make things weird for gods, but I like to think that several gods are just different names to different planes. You know, the ol' Takhisis vs. Tiamat idea. That's why I wasn't afraid to let PCs use gods NOT from our homebrew pantheon 
They either manifest differently, or their ideas/ideals are different based on the different realm's customs, inhabitants, and whatnot!
(admittedly, my way is a very lazy way, since I just let everyone else make up all the lore for me and I just focus on Endermor. But it's also severely inclusive. So that's a win in my book!)
Timborama wrote:
My work follows an Axis Mundi / World Tree / World Axis model as well, though it's also well envisioned in a "real world" sense, with the Astral Sea and Far Realm representing "outer space" while the Underdark and Elemental Chaos and Abyss represent an "inner space," a world of churning creative destruction within the heart of every world. To them, worlds are born out of crystalized chaos, contained within the chaos, essentially motes of order floating within the Chaos, with the Astral Sea a lattice of order made up of systems surrounding motes. But to an outside observer, the chaos is something within, like another world piercing through the heart of every star and planet, with every black hole a gateway into the dark Abyss at the heart of the chaos.
The Feywild and the Shadowfell are parallel world, worlds that might have been or perhaps were, with this version fo the world being a might-have. In the Shadowfell setting of the world, the world is torn to pieces, it is the torn world, destroyed by the humanoids greed and wanton desires. The survivors work their way on a darkened, smogged shattered planet, filled with the stench of deaht, just trying to survive. In the Feywild, on the other hand, such terrors never happened, and the world is as it was in the twilit morning of the world. The Feywild and Shadowfell are sort of fused with the plane of dreams; the Shadowfell is also known to cross into people's nightmares, with their spirit forms entering it through nightly terrors, while the feywild inhabits dreams of another world and age as well. Some say that the Feywild is a memory of how the world once was, while the Shadowfell is a foretelling of how the world will be, after the end.
Oh! It's also worth noting that in my "anything's possible" style, the Elemental Planes are infinite, essentially, similar to the infinite layers of the abyss, and include things that aren't strictly elements (scientifically speaking, and also speaking of ancient lore/mysticisms). Sure the "biggest" ones (in size, power, and the knowledge pertaining to it) are air, earth, fire, and water, but we also have elemental planes of wine, grass, wood, cold, stuff like that. Because they are infinite, there is overlap between all layers at some point, so this is how the (semi)plane of Ice exists, as an overlap between Water and Cold.
I was inspired by this when the descrption of the Endless Decanter of Water says that it taps into the Elemental Plane of Water, essentially opening a mini portal. So I figured, why isn't there a Elemental Plane of Beer? And WITHIN those planes, why aren't there demi and semi planes of dark stouts, pilsners, and even PBR? Yes beer isn't an element, but why can't we have an entire plane dedicated to a roiling sea of desert wine?! Why can't I summon a Marinara Sauce Elemental? Why can't this bag of holding open up to a demiplane in the plane of cold, so we can chill our beverages (special thanks to those Coors Light commercials for basically stealing this idea!). So I did. And we do.
So, essentially, if it's a thing, there's probably an "Elemental" Plane of it.
Elemental Plane of Snot.
It's that simple.
Edit: Loving these threads BTW
I like to add the mirror plane, (like Alice's tale), "fighting" againts the shadowfell.. like the second one was a "infectation" of the first.
Other idea is the time spheres. They are like parallel world, a different timeline, for example a Krynn without cataclysm or Arthas with gods.
For low level characters I have got elemental demiplanes where exploration is easier.