Inner Planes

The Inner Planes consist of the elemental, demielemental, quasielemental, and paraelemental planes.

The four main Inner Planes are:

The Plane of Elemental Earth
The Plane of Elemental Fire
The Plane of Elemental Air
The Plane of Elemental Water

These planes are home to the various elementals that wizards and the like are able to summon to fight on their behalf. There are theories that these planes contain entire civilizations that rival anything known, but due to the extreme conditions within those planes, it is virtually impossible for this to be verified (and, as a Traveller would say, the elementals aren't talking).

Planar shifting directly into these planes, even with proper protection, is generally an expensive and quick death; as the Elemental Planes are the epitome of their respective domains, the Plane of Elemental Air, for example, would be a torrent of zephyrs, tornadoes, hurricanes, such as never before encountered.

It is generally considered that any magical or nonmagical protection against the elements simply does not function within the inner planes, due to the severity of the conditions contained therein.

In addition to the four main Inner Planes, there are a multitude of various quasi-, para-, and demielemental planes (such as the Quasielemental Plane of Salt, Demielemental Plane of Ash, etc.); any combination of dust, crystal, ice, minerals, lava, and so on and so on that can be imagined has its own little plane. It is unknown whether the demielemental planes are contained within the four main Inner Planes or very nearby, but they exist.