*The Planes are big.*
Really big. In fact, many of them are infinite. In fact, many of them contain smaller infinities within them. To make this all the more confounding is not all of these planes adhere to the normal sense of 4-dimensional space/time of the Prime Material. Confused yet? Good, that's normal. If you are a Prime, this can take quite a while for you to really grasp, but if you are a Planar, then all this is so second nature to you that such questions are either pointless or a point of philosophical standing. One way or another though, you are here to be educated on them. Below, you will find a basic guide to everything you need to know about the Planes. This, however, is not a comprehensive guide, for that you are going to have to actually get out there and walk the planes, berk!
*Basic Terms*
Well, before you can really start to understand the Planes, your need to know what the planes basically are and a few subsets therein.
*Plane:* A Plane is an infinite expanse that usually represents a certain physical element, alignment, or ideology, and maintains its own set of physical laws, environments, and native beings. For example Baator, or the Nine Hells to those clueless primes, represents the concept of pure Law and pure Evil.
Simple right? WRONG! There's more to it than you might at first think!
*Layer:* A Layer is portion of a Plane that is linked to other layers in a variety of manners. In and of themselves, Layers are usually an infinite expanse that is representative of a certain sub-set of the concept that the Plane. Continuing the example above, Baator has 9 layers, each infinite in and of themselves, but accessible to one another through a variety of gates and guarded passages.
Lets get a little smaller now shall we?
*Realm:* A Realm is a portion of a layer that is unified by very specific conditions and natives. Generally speaking, a Realm is the home domain of a Power (a deity) and is controlled entirely by that Power . While finite, the size of a Realm can still be very great depending upon the might of the Power. Continuing on with Baator, Kurtulmak (The racial deity of Kobold) lives in his own realm of Draukari on Avernus, the first layer of Baator. While most of Avernus is a blasted hellscape, Draukari is a series of hills and forests filled with deeply dug barrows that Draukari and his petitioners dwell within.
Of course, the smallest unit you get to are cities, towns, and such things that exist as normal. Here's a few more definitions to help sort things out as we go along.
*Prime Material Plane:* This is where most of you berks are from, the Prime is made up of countless Crystal Spheres that float through an infinity of Phlogiston, a sort of high-energy liquid and air-like substance. Each Crystal Sphere holds within it the universe of a different campaign setting. Ebberon, Toril, Kyrnn, Athas, Oerth and more are just floating away here. Something special about the Prime is that folks here are made up of two parts, the physical and the spiritual, their bodies and souls make up two different albeit connected units. You'll see why this makes such a difference.
*The Inner Planes:* The Inner Planes are better known to some as the Elemental Planes, each of which represents an element in its idealized form. There are 6 main Inner Planes that "orbit" and contribute to the elements of the Prime Material Plane. These are the planes of Fire, Water, Earth, Air, Positive Energy, and Negative Energy. While these planes are infinities unto themselves, some of them touch slightly to produce Para- and Quasi- elemental planes, which will be discussed further below.
*Outer Planes:* The 17 Outer Planes make up the Great Wheel, the Cosmological model of the Planescape Multiverse. Each of the Outer Planes represent a certain alignment and ideology in varying levels. These realms, and their native inhabitants, are different from the Prime in that their bodies and souls are not distinct elements. Rather the Outer planes and their inhabitants are made partially out of "real" substance and partially out of belief. Almost all mortals will eventually travel to one of these Outer Planes, as the Outer Planes actually function as the afterlife of mortals. Depending upon a person's beliefs and general manner throughout life, their soul is sent to one of these planes after death, either to the realm of the deity they worshiped or to a more general layer that represented them. These souls, called Petitioners, are often the basic building blocks from which certain Outsiders come from. A Lawful Good person who dies is likely to go to Mount Celestia, and after a certain time (depending upon their strength of soul and deeds performed in the afterlife) they may ascend to become an Archon (a sort of angelic being.) On the flip side, a Chaotic Evil person is likely to be sent to the Abyss, where they will be turned into a hideous Larva to be eaten, tortured, and generally harassed with the lucky(?) few managing to eventually become Demons.
*Transitive Planes:* The Transitives are a strange bunch of planes that exist as connecting points between other planes. Because each transitive plane is fairly unique in how they work, I will be going over them in more detail in their individual sections.
*Demi-Planes:* A Demi-plane is a finite plane that is often an artificial creation of deities/Powers, especially powerful wizards or psions, or occasionally broken off fragments of another plane. Most of these Demi-Planes exist as self-contained bubbles that float through the deepest parts of the Etheral Plane. Examples include the famous Demi-Plane of Dread, Ravenloft, and the Living Plane, Neth.