The Underworld

The Underworld underpins all the various Material Planes, and is the respository for the collective hatred, despair, spite and other evil thoughts and emotions of all sentinent inhabitants of the Material Planes.
It mainly consists of a seething ocean of raw chaos, in which small islands of structure can form and last for shorter or longer periods of time, depending on the willpower of an individual that creates them, or the pervading continuity of a particular emotion or feeling. This is the realm of demons - creatures of spiteful chaos that live for the destruction of all order.
At the centre of the Underworld, if it can be said to have a centre, there is a permanent island of stability. This is Hell - the realm of the devils - an order of creatures that thrives on sentient despair. The very existence of Hell within a sea of chaos is because its inhabitants rigidly adhere to a set of rules that are always followed to the letter. It is suggested that if a devil were ever to break a rule or contract, then all of Hell would be at risk of dissolving into the chaos.
Hell is constantly under seige from waves of demons that emerge from the chaos that laps on every side of it.

Type

Plane of Existence