The 666 layers of the Abyss are an estimate, but the Abyss definitely has the most layers and therefore potentially the most inhabitants of any of the outer planes. No sage or scholar claims to have visited or catalogued each of the layers. Each Power seems to claim at least one layer of the Abyss as its own, making further definition difficult. The thought of an infinite number of infinitely large planes boggles most minds, so the estimate of 666 layers is generally used.
The Abyss combines all that is evil with all that is chaotic to produce an ugly, violent plane where the strong survive only on the backs of the weak. It is the birthing place of the demonic races, and is called Demonholme by the natives of Gladsheim and Jurgarten (misshapen lands) by those of Arvandor.
The only layer of the Abyss that is well known is the first layer that is called Pazunia (for Pazuzu, who is most often found here), the Plains of Infinite Portals, or the Palace of 1,001 Closets. The layer is the topmost of the uncountable Abyssal layers. It is a barren, dusty place without life or greenery, baking beneath a hellred sun. The dusty plains are broken by three features: huge holes in the earth, great iron portals, and the river Styx. The holes of this first layer are conduits to the various layers of the Abyss.
These function like conduits in the Astral plane in that those who descend are immediately taken to the layer the conduit leads to. The iron fortresses usually house the material bodies of higher level demons and demon lords when they are traveling astrally. The iron fortresses are usually guarded by the demon’s servants who fight to the death (permanent in this plane) to protect their lord’s body.
Demons sometimes war against each other while one is away on the Prime Material plane, seeking to slay their enemy’s physical form and either kill the Power or maroon it on a Prime plane. Sieges are common in the first layer of the Abyss. Demon lords expend much energy fortifying their strongholds against attacks. They return as soon as possible if given word that their true body is in danger. The river Styx flows in a winding course across the top layer of the Abyss.
Some channels of it pour into holes, while other portals feed the river of forgetfulness with waterfalls that run in reverse. Travelers are advised to use the boatman Charon or his servants when journeying on this river. A character thrust into a random layer of the Abyss (either through curse, item, or choosing the wrong conduit) can find himself in any of a number of terrains. These terrains stretch on forever and are inhabited by all manner of foul creatures.
The interplanar portals on the topmost layer of the Abyss also look like large holes, creating havoc for the traveler seeking to pass through the Abyss to other destinations. Most travelers avoid this method. The iron fortresses are usually immune to the effects of astral viewing portals, so that astral travelers cannot enter the iron fortress from the Astral plane. No known barriers exist in the first layer of the Abyss. Those that are known in other layers are jealously guarded by the inhabitants of those layers. Barriers can be located in any terrain in the Abyss and can lead to any terrain on the other side.
The most numerous of the creatures of the Abyss are the demon races, a fell group of foul monstrosities seemingly limitless in number. Their prolificacy would cause concern in other planes were it not for the fact the demons always turn on each other. The stronger always seek to dominate the weaker, and the weaker always conspire to overthrow the stronger. Alliances mean little in the Abyss, for the demonic allies of one moment become the enemies of the next.
Rulers of the various layers often maintain vast standing forces in their home layers. The demons lords are the most powerful of their race. Each demon prince controls one or more layers of the Abyss, but they are continually at each other’s throats with plans and counterplans to expand their domains.
The only unifying force is their hatred of good and organized peoples. The exact layers inhabited by the demon princes are unrevealed. This is left for the traveler to discover.
The rumored dwellings of the demon princes are as follows:
• The dwelling of Orcus is a great palace made of bones, rising out of ground bone meal. His guards and servants are undead. From his empty halls Orcus rules many layers and is said to have conquered a number of Prime Material planes.
• The realm of Demogorgon spans several layers, yet each is a jungle filled with dinosaurs, wild apes, and bird-like monsters in addition to the standard complement of demonic life.
• Yeenoghu’s great mansion is the size of a city. It rolls across the barren salt-waste of his layers, pulled by slaves and controlled by gnolls.
• Juiblex has a layer made of living fungus and rot. Here all matter is decaying and all manner of slimes and molds live off each other’s putrid forms.
• Lolth controls a number of adjacent planes but is reached through a great web built in the midst of a primal maelstrom.
• Baphomet lives at the center of an infinite maze that spans his layer and the layers adjacent to him. The maze is said to change as it passes between the layers. It is rumored to be populated by all manner of minotaurs, some of whom have breath weapons and magical abilities.
• Fraz-Urb’Luu has only recently returned to his home realms. He is still in the process of removing those lesser creatures who usurped his domains during his absence. At its height, Fraz- Urb’Luu’s realms rivalled the beauty of those of the Twin Paradises or Arvandor, but this is only a cruel deception, for beneath the illusion is decay and rotting flesh.
• Graz’zt makes his domain in a great palace that fills an entire layer and dominates the nearby layers of lesser demon lords. Here Graz’zt marshals his army against the forces of Orcus and Demogorgon.
• Kostchtchie’s domain is only part of a single layer, but the hatred of this demon prince spans the layers of the Abyss. His plane is a glacial place, filled with all evil creatures of cold.
• Pazuzu has no abode, but is ceded the air above the surface of every layer of the Abyss. The demons depend on Pazuzu (and to Charon in those layers where the Styx runs) for ready transportation, making him that rarest of beings, a well-liked (or at least tolerated) demon.
• Zuggtmoy has several realms scattered among a number of layers of the Abyss. In general, they appear as normal environments overrun by fungus and lit by a purplish light. All manner of fungoid creatures inhabit the realms of Zuggtmoy.
Demon lords and princes are considered Lesser Powers in their home planes. If slain in the Abyss, they are dead (though another creature will evolve into a being similar to the deceased demon to fill the gap).