Inner Planes

Combined, the energy and elemental planes form two larger, recursive planes, with each plane being a sub-plane of the bigger energy and elemental plane. If you could walk in a strait line, you could walk all the way through the Positive Energy Plane, pass through the Realm of Twilight, enter and walk through the Negative Energy Plane, pass through the Realm of Twilight again, and find yourself back in the Positive Energy Plane. The same is true of the elemental planes, minus the Realm of Twilight. Each plane itself is bounded. The boundaries of the energy planes are fairly easy to tell, as each plane is composed of a "land mass" and sky, much like the material plane. The boundaries of the elemental planes are a little more difficult to discern as those planes are more amorphous, being largely composed of the element dominating the plane.

The border area between the Positive and Negative Energy Planes is known as the Realm of Twilight, and it is a planar region of utter strangeness, where the positive and the negative mix, creating things that can't even be imagined.

The borders between the different elemental planes are chaotic, where the two elements mix to create unique and frequently destructive creatures. At the apex where all fours planes meet, true chaos reins and almost anything is possible.

None of the inner planes have layers.

The energy planes are subject to normal gravity, as are the Planes of Fire and Earth. The Plane of Air is subject to subjective gravity, while the Plane of Water largely doesn't have gravity. Creatures in the Plane of Water basically swim where they want to without bouyancy.

As described on the Cosmology page, all planes are at least somewhat mutable. The energy planes are very difficult to exert any real influence over; the gods of those realms like things the way they are. The elemental planes are probably the most mutible planes of all; these realms were created to be molded and influenced and the gods of these realms do little to interfer with other's creations.

Plane of Air

Plane of Earth

Plane of Fire

Plane of Water

Negative Energy Plane

Positive Energy Plane

Realm of Twilight