Pandemonium (Dungeons & Dragons)
In the standard cosmology of the Dungeons & Dragons fantasy role-playing game, Pandemonium (or, the Windswept Depths of Pandemonium) is the Outer plane where Chaotic Evil and Chaotic Neutral petitioners are sent after death. Pandemonium is a large, complex cavern that never ends. Compounding this problem, howling winds drive most of its residents mad. There are few creatures that are native to this plane; those individuals who do live there usually have no choice in the matter. It is one of a number of alignment-based Outer Planes that form part of the standard Dungeons & Dragons (D&D) cosmology, used in the Planescape, Greyhawk and some editions of the Forgotten Realms campaign settings.
In the Planescape campaign setting, Pandemonium houses the headquarters for the Bleak Cabal faction.
The plane known as Pandemonium was mentioned for the first time by name in the article "Planes: The Concepts of Spatial, Temporal and Physical Relationships in D&D", in The Dragon #8, released July 1977. The plane was mentioned again in an appendix of the known planes of existence in the original (1st edition) AD&D Players Handbook, published in June 1978, where it was described as "The Planes of Pandemonium of chaotic evil neutrals".
Each of the four layers of Pandemonium is successively deeper within the caverns.
Pandesmos is the largest and (relatively) most hospitable of the layers. The headwaters for the Styx are found here.
Cocytus is also known as the "layer of lamentation", for this is where the winds are the strongest.
Cocytus is the location of a number of godly realms, including the god Erythnul's realm of the Fields of Malice, the bugbear deity Hruggek's realm of Hruggekolohk, Cyric's realm of the Shattered Castle.
Phelgethon is the location of a number of godly realms, including the Queen of Air and Darkness's realm of the Unseelie Court, Zeboim's realm of The Maelstrom, and the derro deity Diirinka's realm of Hidden Betrayal.
Agathion is the deepest area of Pandemonium and is generally sealed off from the rest of the plane. Where Pandesmos has wide-open caverns, Agathion has narrow caves that eventually dwindle to pocket spaces within the infinite rock. It is said that deities use these sealed off areas, which are nearly impossible to get to, to store indestructible artifacts or deity-level monsters that could not be killed. Entry to these pocket areas is notoriously hard; each space only has one portal in and out, while some areas are so ancient that their portal could have been destroyed eons past.
- Larme, John. Dangerous Games? Censorship and "Child Protection"  (2000).
- UO-Planescape: Pandemonium (Italian) page from Planescape Italian fansite