The Abyss

A world with no known boundaries, and a tenuous prison keeping a flood of demons from the Material Plane.

Geography

The geography changes to the whim of the strongest demons around. It changes even faster than the Shadowfell and the Feywild: a demon lord can assemble a kingdom simply by walking through it, and even lesser demons can sculpt the landscape like clay. It's futile to draw a map of the Abyss, since it becomes obsolete almost immediately. The only way to navigate is by using magic to locate a specific demon, or using auguries to glean general information, like the location of the nearest portal to the Material Plane.

Fauna & Flora

The flow of demons to other planes is finite, but within the Abyss, the demon population is effectively infinite. Their ecology is always changing, making sure that no part of the Abyss is safe for long. In addition to their endless numbers, demons can always regenerate from death, unless they're killed by a non-demon while in the Abyss. Because of this, non-demons are extremely unwelcome here.

Type

Dimensional plane