Pandesmos

Pandesmos was the topmost layer of the plane of Pandemonium in the Great Wheel cosmology. Most of the gods who claimed their realms in the Windswept Depths made this layer their home.

Description
Pandesmos was the most hospitable layer of the plane. The caverns were the largest here,  some literally thousands of miles across. Immigrants to Pandemonium tended to live on the surfaces of these massive caverns, which contained both cities and citadels, though these were very rare. Most caverns were abandoned to anything but wind. Despite the size of the caverns, they were as loud and windy as the rest of the greater plane. Entire nations could fill the cavern walls, but the strong winds prevented this from ever happening.

The Styx began here, fed by countless cold streams flowing along the walls of the otherwise rocky, subterranean wastes. Some of the streams even floated through the open space in the centers of the caverns.

Dead-end tunnels with unusually strong winds (even for Pandemonium) often signaled that one was at a barrier and about to pass to the lower layer of Cocytus. Flat, square portals found in Pandesmos led to Limbo, the first layer of the Abyss and the Outlands. Yellow squares led to Limbo, red squares to the Abyss, and black to the Outlands. The portals were inconsistent, however, and sometimes sent travelers to the wrong planes.

To reach Pandesmos with the planar shift spell required an iron planar fork tuned to the note of C♯.

Locations
One of the rare cities in Pandesmos was the Madhouse, a citadel controlled by a group of outsiders called the Bleak Cabal. The Madhouse was often used as a way point for travelers to Pandemonium. It was a sprawling city of poorly arranged buildings covering all of the walls of a large cavern. The citadel was divided into sections by multiple stone walls. Befitting its name, a high percentage of the residents of the Madhouse were deaf or insane or both.

Deep in Pandesmos was found a cave where the never-ending winds had worn down the walls until they were as smooth as glass, forming a chamber of mirrors. This Cavern of the Self was full of a magic that caused one to see her or his reflection hundreds or thousands of times. Each image, however, was of the viewer from different time points in life and expressing different emotions, and one only ever saw him- or herself, never an image of any companions. It was believed that if one could find her or his true reflection at that instant among the plethora of reflections, great personal insight would be gained.

Realms

 * Auril's palace of Winter's Hall was located here.
 * Raxivort maintained his Black Sewers somewhere in Pandesmos.
 * Talos had his Towers of Ruin located on this layer.