Austin's Planar Cosmology
Austin is far from the only realm that is known to exist. In addition to the various planets, moons and stars that make up the universe it is part of, there are numerous other "universes" that exist parallel to it. We call these other realms of existence Planes of Reality, and they are very strange places indeed. Not governed by the same laws of reality that apply on Austin (like breathable air, gravity, night and day etc), they are places out of dream and nightmare, home to bizarre creatures, some of which have designs on our world. Here too, can be found the home realms of the gods themselves. It would be futile for me to try and list every Plane that there is, they outnumber the stars in the night sky. However, some are certainly much more important in terms of their relations to our planet, and so I will concentrate on detailing them.
Chandler - Archmage and Planeswalker
The Core Planes
Material - This is the Plane that we call our universe. It is mostly empty vacuum, dotted with great balls of fire called stars, around which orbit balls of mass we term planets. The Material Plane is unique in that it is comprised of something of everything, as oppossed to being dominated by one feature or element. To the best of our knowledge, only the planet Austin supports life (though I find this impossible to believe myself).
Ethereal - This is where ghosts come from, and it is the source of the negative energy that empowers the undead. Suffice to say, it is a creepy dimension of mists and fog, home to many undead creatures. The Ethereal Plane is a surreal mirror of our own, featuring the same places, but subtley twisted to look darker and more menacing. Because of how easy it is to travel from this realm to the Material it influences the other considerably, most notably the subconscious, as when dreaming it is easy to "see" this realm, and such visions are the cause of many nightmares. The Ethereal Plane itself is not evil, but many evil things dwell here.
The Inner Planes
Earth - An unending series of massive caves and tunnels, with no sunlight or even a surface to ascend towards, Earth is a very confusing place to visit, as there is literally no up or down. In some of the more massive caves, there are cities that cover every surface of the caverns interior, floor, walls and roof! This is the home realm of Earth Elementals, the Dao Genies and numerous other stone based creatures. It is believed that Toris summoned the Umber Hulks that endlessly dig Austin's underdark from this plane. This Plane is also the wealthiest place in the multiverse, as gemstones and precious metals can be found in massive seams here. This plane is home to the dwarven gods Clangeddin and Berronar, and their followers spirits who arrive here truly believe they are in paradise.
Air -
Fire - The Great Inferno, and possibly the source of the raging balls of fire that we call stars, Fire is the most unforgiving of the Outer planes and is home to the Efreet Genies, cruel beings all of them, and their Fire Elemental servants. It is impossible to visit this Plane without extreme magical protection, or immunity to fire.
Water -
Astral -
The Outer Planes
Abyss - Arguably the best known of the Outer Planes, due in the main part to the invasion launched from this place in 1427 by the Tanar'ri forces of the Goltari known as Graz'zt. This is a massive realm, home to numerous gods and other powerful beings of chaos and evil including at least 2 other Goltari (Horned Rat and Lehesa). Each of these powerful denizens of the Great Pit maintains control over a sizeable realm or stronghold such as Castle Malevolus or the Demonweb Pit. The creatures of the Abyss are universally termed Demons and they are hostile to any outsiders visiting their Plane. The rulers of this plane, scheme eternally to wrest power from each other, but more than a few have interests on the Material Plane too, and they are not shy in sending their minions to terrorise the mortals of Austin.
Hell - Known as the home realm of the lawful evil devils and their lords, Hell is also home to several gods, most notably Tigress Silverclaw! The creatures of Hell are termed Devils and they are the diabolical opposite of the Demons of the Abyss in every way. The two races cannot abide one another, and they clash whenever they meet. this does not stop the devils coveting power on the Material Plane though, and they once marched under the banners of the Demon Lord and his Geomancer generals across Austin, until they were defeated. Millennia later, they still wait a chance for revenge on the peoples of that world who defied them!
Elysium -
Paradise -
Limbo - The Great Nothing. Limbo is just a huge empty space. If you can, imagine the Material Plane but without any of the stars, planets, comets etc that are scattered across our universe. There are realms here, but none of them are native, having been made made from materials brought from other planes (mostly from Earth). They appear as islands floating in a sea of nothingness, and almost all of them are home to gods or powerful mortals who have come here to be alone, and so they do not welcome visitors.
Other Planes
Beyond - I have no other name for this place only to say that it is indescribably vast. Strangely, despite being so far removed (in planar terms) from the Material, it is very easy to listen in and scry our reality from this one. I believe that this place is where the Entities came from who helped us to win back our world from the Demon Lord and his hordes, and where I suppose they have now returned to. In the short visit I made to this place, I saw nothing in the way of features or terrain, just a great multicoloured ever-changing empty void.
Dominion - This is what I term the plane that Toris accidentally opened a portal to and in doing so opened a route for the Mindflayers to invade our world. Thankfully my brother Gwydion was able to seal off that conduit to this horrid realm, where every mind is held in total thrall to the Illithid God Brains. Still, it worries me that the creatures of this plane now know of Austins existence...