Each D&D campaign setting’s cosmology is composed of many individual universes, or “planes.” The Material Plane is where “normal” campaign settings are located. In 2nd Edition, all the “normal” campaign settings such as Greyhawk or Forgotten Realms existed on different planets on the same Material Plane. In 3rd Edition, Greyhawk and Forgotten Realms exist on different Material Planes, and, indeed, in completely separate cosmologies. The “standard” cosmology is the one associated with Greyhawk in 3rd Edition, so that’s the one I’ll discuss.
The Ethereal Plane occupies the same space as the Material Plane, but in a different dimension. Creatures on the Ethereal Plane can see and hear Material creatures, but not vice versa. In fact, Ethereal creatures can pass through Material objects and creatures as if they weren’t there. If you’ve seen the episode of Star Trek: TNG where Geordi and Ro are affected by the Romulan “phase cloak”, that’s exactly the same thing. It is possible for Material beings to cast spells allowing them to see Ethereal beings, and spells that use magical “force” (such as wall of force) affect Ethereal beings normally.
The Astral Plane is the void which lies between the other planes and allows them to connect to each other. Any time someone uses magic to teleport, they’re travelling instantaneously through the Astral Plane.
The Plane of Shadow is a plane of perpetual gloom and twilight. It exists alongside the Material Plane and can be used as a planar “shortcut” to travel long distances across the Material. Also, many spells use Shadow energy to create effects that are part illusion and part real. Finally, it may be possible to use the Plane of Shadow to travel between the Material Planes of different campaign settings.
Next, there are the Inner Planes, which are the planes of **Earth, Air, Water, Fire, Positive **(life) **Energy, **and **Negative **(death) Energy. In 2nd Edition, there were also “paraelemental” planes where the elements mixed with each other, and “quasielemental” planes where the elements mixed with either positive or negative energy. The most powerful inhabitants of the Inner Planes are the elemental genies.
After that, there are the Outer Planes, which are the planes of morality and ethics. Most of the gods live on these planes, and most of their worshippers go there for the afterlife. If you imagine good as “up”, evil as “down”, order as “left”, and chaos as “right”, then the Outer Planes can be imagined as a big circle. Starting from the “left” and going clockwise, the Outer Planes are **Mechanus, Arcadia, Mount Celestia (Heaven), Bytopia, Elysium, **the **Beastlands, Arborea, Ysgard, Limbo, Pandemonium, **the **Abyss, Carceri, Hades, Gehenna, Baator **(Hell), and Acheron. There’s also another plane in the “center” of the circle called the Outlands. Many of the Outer Planes have several “layers”, which are to the planes like floors are to a building. Baator, for instance, has nine layers, each of which is ruled by a Devil Lord.
At the center of the Outlands is a Spire which is said to be infinitely tall. Despite this, there’s a city which is said to be on the “top” of it. This city is called Sigil, and it is the heart of the Planescape campaign setting. Sigil is built on the inside of a half-torus, so the horizon curves upward. Sigil is called the City of Doors because any doorway in the town has the potential to be a magic portal to another plane. A portal only works, however, if the person walking through it has the proper “key”, which could be an object, a creature, a word, or virtually anything else. Sigil is governed by various factions which are each devoted to a different philosophy; however, the true ruler of the city is The Lady of Pain, a mysterious being who is rarely seen unless something threatens the city’s neutral balance. In that case, she’s the last thing they’ll see, because she can flay the skin off a person with a glance. For lesser threats, she imprisons the offender in a Maze, which is a type of demiplane (see below.) A Maze endlessly twists and turns back on itself, but there’s always a way out hidden somewhere. It is said that The Lady savors the anguish of a prisoner who knows there’s a way out, but who is doomed never to find it. Even gods cannot defy the power of The Lady, for her law forbids any god to enter Sigil. (Priests, however, are still perfectly welcome.)
Sigil may be the best way to travel between planes, but it’s not the only way. There are also various “paths” that connect different Outer Planes together. The good (or “Upper”) planes are connected by the River Oceanus, while the evil (or “Lower”) planes are connected by the River Styx. There’s also the Infinite Staircase, which is a chaotic jumble of Escher-like stairways that lead to any place where intelligent beings use creative thought. It is said that if you wander the Staircase long enough, it will lead you to your heart’s desire. In 2nd Edition, there was also Mount Olympus, which connected Arborea, Carceri, Gehenna, and Hades with every world where the Greek gods were worshipped; and Yggdrasil, which connected the realms of the Norse gods.
In addition to all that, there are also various demiplanes, which are like planes, except they are of finite size. Powerful wizards often create their own demiplanes to use as secret fortresses. In 2nd Edition, the Plane of Shadow was actually a demiplane. The campaign setting of Ravenloft is located in a hidden demiplane ruled by mysterious beings called the Dark Powers. Ravenloft is like a cosmic Roach Motel: anybody can enter, but nobody can leave. It’s divided up into various “domains” which are ruled by evil beings known as “darklords.” Most darklords are similar to Gothic literary villains such as Dracula, Dr. Jekyll, Frankenstein, and so on. When a person commits enough acts of irredeemable evil, the Dark Powers turn him into a darklord and give him great power over his domain, but they also curse him to be forever denied that which he desires most. A darklord can usually seal the borders of his domain with some kind of unbreakable magical effect, but he can never cross those borders no matter what. Of course, these darklords all have lots of loyal minions, such as vampires, ghouls, ghosts, and werewolves. In Ravenloft, every day is Halloween, and you are the treat.
That’s all there is to the standard D&D cosmology. Of course, if that’s not enough for you, there are always optional planes you can add, such as the Plane of Dreams, the Plane of Mirrors, the Elemental Plane of Wood, or the Far Realm. And, of course, I haven’t covered all the different planes in other cosmologies, such as Forgotten Realms or Oriental Adventures. If you want to know more, you can always do what I did: spend years memorizing every miniscule detail in every Planescape product ever published. Only then will you achieve the title of D.D.D. (Doctor of Dungeons and Dragons.) For your convenience, PDF files of these products can be purchased at www.svgames.com. Good luck!
Hey, this was just a few years after the Conan movies came out.