The Abyss

The Infinite Layers of the Abyss make up a single outer plane, more commonly referred to as simply 'the Abyss'. The Abyss is a remnant of the former plane of Malumbris, which split into the Hells and the Abyss during the First Era. The Abyss, together with the Hells and Gehenna, are known as the Lower Planes. The Infinite Layers of the Abyss is a Chaotic-Evil aligned plane.

Inhabitants
The Abyss is inhabited by a race of fiends known as demons. Most of the layers of the Abyss are ruled over by an Archdemon or Demon Lord, though this is not always the case. The demons will assemble large armies to fight devils in the Blood War, but more often than not will end up fighting each other as they vie for power and attempt to establish supremacy over other demons.

Society
The Abyss is impossible to characterize generally. Layers can vary from dense cityscapes to wild, open plains, to icy, frozen tundras, to dense jungles. Furthermore, because of the plane's (theoretically) infinite nature, it is likely that any possible environment has already been formed there.

Layers
There are an infinite amount of layers in the Abyss, and, as a result, it would be impossible to name all of them here. Some of the more important ones have been afforded brief descriptions.

Layer 1: Pazunia
Ruled over by the Demon Lord Pazuzu, Pazunia is a barren wasteland marred by scorching winds under a relentless red sun. The surface contains dark pits that contains portals to many of the other planes.

Layer 23: The Iron Wastes
The Iron Wastes is home to Kostchtchie, the Archdemon of Rage. It is a vast expanse of glaciers, mountains, and ruins buried in ice and snow.

Layers 45, 46, & 47: Azzagrat
Azzagrat, the realm of the Archdemon Graz'zt, actually spans three separate layers of the Abyss. The city of Zelatar spans all three layers, and houses the Argent Palace, Graz'zt's seat of power.

Layer 66: The Demonweb Pits
Home to Lolth, the Spider Queen, the patron of the Drow, the Demonweb Pits is an immense network of massive spiderwebs that lies above bottomless pits.

Layer 88: The Gaping Maw
The Gaping Maw is the home of the Archdemon Demogorgon. It consists of a vast continent covered in jungle surrounded by an endless ocean and brine flats.

Layer 89: The Shadowsea
The Shadowsea is inhabited by the Demon Lord Dagon. It is a deep and perpetually dark ocean.

Layer 96: Invidia
Invidia, home to the Archdemoness Zelas, Invidia is a beautiful plane containing mountains and cities with crystal spires. The mountains contain deep, incredibly treacherous mines filled with precious gems

Layer 113: Thanatos
Thanatos is the home of the Archdemon Orcus. A land of ruin and death, Thanatos contains the Everlost Palace, Orcus's seat of power, a vast castle made of obsidian and bone.

Layer 128: Slugbed
Slugbed is the home of Puhel, the Archdemon of Sloth. It contains a vast expanse of forests, shallow seas, and underground caverns, perpetually covered by fog and darkness.

Layer 176: Hollow's Heart
Hollow's Heart is a layer home to the Archdemon Fraz-Urb'luu. It is a constantly-shifting place of fantastical natural features that defy the natural laws of the universe. Nothing is as it seems in Hollow's Heart, and it is said that Fraz-Urb'luu can control the makeup of the layer with a mere thought. Because of this, some scholars theorize that the entire layer is actually an incredibly well-crafted illusion.

Layer 222: The Slime Pits
The Slime Pits is where the Archdemon Juiblex makes his home. The Slime Pits is a bubbling, fetid swamp, covered with oozes, molds, and slimes. All material from the layer is made of slime and ooze.

Layer 223: Offalmound
Offalmound is ruled over by the Archdemon Eken. The entire layer is made from rotting organic material, and any food brought there will rot in a short amount of time.

Layer 243: Vastita
Ruled by the Archdemon of Pride, Urek, Vastita is a massive realm with enormous castles and wealth. Urek rules over the layer with an iron fist, and frequently puts his populace to work constructing massive buildings and sculptures.

Layer 333: The Broken Scale
The Broken Scale is a massive open market ruled over by Tiyn, the Archdemoness of Greed. Nearly any item in the universe can be bought and sold here - no legal regulations apply. Tiyn's forces ensure an uneasy peace over the location, but can frequently be bribed to allow the rules to be bent.

Layer 386: The Bloodlands
Home to the Archdemon Morgath, the Bloodlands are a war-torn battlefield. It was once said to be a beautiful paradise, but now is covered with death and decay. The name comes from the water, which has been appears red in color.

Layer 422: The Death Dells
An endless hunting ground of barren hills and ravines, the Death Dells is home to the Archdemon Yeenoghu. It is populated primarily by gnolls, hyenas, and ghouls.

Layer 471: Androlynne
Androlynne is the home of the Demon Lord Ozundyla (better known as Pale Night). Ozundyla turned the realm into a prison for celestials, and the creatures' influence has turned the realm into a surreally beautiful and alien place.

Layer 570: Shendilavri
Home to Yelea, Archdemoness of Lust, Shendilavri is a beautiful realm of grassy hills on the shore of an ocean under perpetual sunset. Yelea's seat of power is in the city of Rivenheart, which is said to contain all possible pleasures and desires.

Layer 600: The Endless Maze
The Endless Maze is the realm of the Archdemon Baphomet. It is - as the name would imply - an infinite maze inhabited by minotaurs, ogres, and goristros.

Layer 663: Zionyn
Zionyn is the home of the Demon Lord Obox-Ob. It is a vast and inhospitable vermin-infested land with oceans of thick resin.