The Abyss
The Abyss is the plane of Chaotic Evil among the Outer Planes and the birthplace of demons.
It consists of an unknown number of layers connected by pits, chasms, rivers, gates, caverns, and other planar passages. No final depth has ever been established. Layers can form, collapse, merge, divide, or change substantially over time, and even well-established routes may eventually become unreliable.
Lessarith the Deceiver has been confined to the Abyss since the defeat of the Triad. Over the ages, her presence, the rise of demonkind, and countless struggles between Demon Lords have helped shape the plane into what it is today.
Structure and Environment
The Abyss has no common landscape.
Its known layers include deserts, forests, oceans, swamps, mountain ranges, frozen wastes, cavern systems, ruined cities, and environments with no close equivalent on the Material Plane. Atmosphere, temperature, gravity, weather, and terrain can differ completely from one layer to another.
Some support extensive wilderness, settlements, fortresses, or entire kingdoms. Others are difficult to inhabit even for demons.
The Abyss is more than simply unstable. Its layers frequently erode, consume, or reshape one another. Territory may be torn away during conflicts, incorporated into another layer, or left behind as fragments within the deeper reaches.
There is no reliable relationship between depth and environment. A lower layer is not necessarily hotter, darker, or more dangerous than one above it, though the least explored regions tend to lie far from the better-known routes.
The Layers
No reliable count of the Abyssal layers exists.
Planar scholars number those that have been reliably identified, usually according to the order in which they entered established records. These numbers are useful references rather than evidence of any fixed sequence.
The Abyss does not remain unchanged.
New layers can emerge from unstable regions, while existing ones may shrink, divide, merge with neighboring territory, or disappear altogether. Some have been destroyed during conflicts between powerful inhabitants.
Fragments of collapsed layers sometimes survive elsewhere in the Abyss, incorporated into other regions or drifting through unstable depths.
For this reason, any catalogue of the Abyss is necessarily incomplete.
Formation and Change
The Abyss existed long before Lessarith's exile, but much of its known character developed during the ages that followed.
Its Chaotic Evil nature allows its layers to respond strongly to the beings that inhabit them. A sufficiently powerful Demon Lord may reshape the landscape, climate, structures, or routes of a claimed domain over long periods of rule.
Conflict can change a layer just as dramatically.
Borders shift, fortresses are swallowed, passages collapse, and territory can be torn from one domain and absorbed into another.
The Abyss also produces life of its own. Demons can arise from the plane independently of Lessarith, while other powerful beings have reached Demon Lord status through entirely different paths.
Movement and Travel
The Abyss has no fixed sequence of descent.
One layer may connect directly to several others, while two regions that appear close together may possess no reliable passage between them.
Portals, pits, caves, chasms, rivers, gates, and other crossings are found throughout the plane. Some remain stable for centuries. Others move, collapse, close without warning, or begin leading somewhere different.
This makes navigation difficult even within well-traveled regions.
The River Styx passes through portions of the Abyss and provides one of the more dependable routes between it and the other Lower Planes.
Travelers who abandon established routes risk reaching a layer with no known means of return.
Connections to Other Planes
The Abyss can be reached through the Astral Plane and through established planar portals.
The River Styx provides connections to the other Lower Planes.
Permanent gates also exist within some of the better-known layers, particularly near major settlements and territories controlled by Demon Lords. Their ownership can change quickly when local rulers are overthrown.
Demonic incursions can create temporary crossings elsewhere. Minor breaches may allow individual demons to pass through, while larger disturbances can produce more dangerous and sustained connections.
Such breaches remain localized planar events. The Abyss does not spread freely beyond its own boundaries.
Demons
Demons are native to the Abyss and exist in more forms than planar scholars have catalogued.
Some emerge from the plane itself. Others arise through transformation or other processes that remain poorly understood.
Many demons remain closely associated with the layer in which they formed, while others travel widely throughout the Abyss and beyond it.
There is no stable hierarchy shared across demonkind.
Power is usually maintained through strength, fear, influence, alliances, possession of territory, or the ability to destroy challengers. A ruler who cannot defend what they hold may lose it regardless of how long they previously commanded it.
Non-demonic inhabitants are also found throughout the Abyss, including mercenaries, cultists, prisoners, explorers, planar travelers, and mortals brought there against their will.
Demon Lords
Demon Lords are among the most powerful inhabitants of the Abyss.
The title carries no divine rank. Demon Lords are extraordinarily powerful beings capable of claiming great territories or entire layers, but they are not deities.
Their origins differ.
Some were deliberately created by Lessarith. Others arose independently from demonkind, developed from the Abyss itself, or reached their present state through other means.
Graz'zt was the first Demon Lord created by Lessarith and remains the one most closely associated with her. He rules Azzagrat, a domain spanning three Abyssal layers.
Demogorgon was her second such creation and later became one of the most powerful beings in the Abyss. His domain is the Gaping Maw.
Pazuzu was the third. His influence is strongly associated with desperate bargains, temptation, and corrupted guidance, while Pazunia, the first widely recorded layer of the Abyss, bears his name.
Other prominent Demon Lords arose independently of Lessarith.
Juiblex rules within the Slime Pits and embodies the endless hunger and dissolution of ooze.
Orcus rules Thanatos and commands vast hosts of undead. Traditions concerning his origins describe him as having once been mortal before rising through demonkind to become a Demon Lord.
Baphomet rules the Endless Maze, while Yeenoghu claims the Death Dells.
Demon Lords frequently war with one another, form temporary alliances, seize territory, and lose it again. Even long-established dominion in the Abyss can end suddenly.
Pazunia
Pazunia is the first widely recorded layer of the Abyss and one of its most common points of entry.
It is a barren land beneath a red sun, scattered with great iron fortresses and enormous pits descending into other regions of the plane.
Many of these pits contain passages to other layers.
The River Styx also crosses Pazunia. Some branches descend into the pits, while others emerge from them before rejoining the main river.
These connections make Pazunia one of the Abyss's most important crossroads.
The layer takes its name from Pazuzu.
The Deep Abyss
The deepest explored reaches contain some of the least understood regions of the plane.
Fragments of collapsed layers can be found there, sometimes still recognizable and sometimes fused into larger masses of unstable terrain.
Expeditions have also encountered creatures that do not match familiar forms of demonic or planar life.
Some regions appear to contain layers still in the process of forming, though few observers have remained long enough to study the process safely.
No expedition has established whether the Abyss possesses a final layer or any true bottom.
The Endless Spiral
The Endless Spiral is Lessarith's divine realm within the Abyss.
It does not occupy a single layer.
Instead, the Spiral extends through the Abyss as a vast network of passages running through its layers. Entrances associated with it have been found in widely separated regions, sometimes hidden within ruins, fortresses, cavern systems, or places controlled by other Demon Lords.
From within, its routes can carry travelers enormous distances through the Abyss.
Passages bend, divide, double back, and descend through chambers whose relationship to the surrounding layers is difficult to determine. A route entered from one layer may eventually emerge into another far removed from it.
Lessarith can alter these internal paths, conceal entrances, open new ones, or leave travelers moving through repeating routes.
The Endless Spiral does not hold the Abyss together, nor does Lessarith rule every layer through it. It is her divine realm and a network extending throughout the plane she has been forbidden to leave.
Lessarith herself is confined to the Abyss as a whole, not to the Endless Spiral.
Natural Hazards
The hazards of the Abyss vary entirely by layer.
Extreme heat, severe cold, poisonous atmospheres, corrosive waters, unstable gravity, violent weather, and dangerous terrain have all been recorded.
Some layers also interfere with perception, memory, emotion, or thought.
These conditions are local rather than properties of the entire plane.
The changing geography creates an additional danger. Routes can disappear, portals can shift destination, and settlements or fortresses may be destroyed before travelers attempt to return.
Old information should therefore be treated with caution.
Survival
There is no single set of precautions suitable for the entire Abyss.
Travelers must prepare for the conditions of their intended destination and any layers they expect to cross along the way.
Food, water, breathable air, normal gravity, and survivable temperatures cannot be assumed.
Reliable navigation is equally important.
Most expeditions rely on known portals, established crossings, the River Styx, or guides familiar with particular layers.
Maps are best treated as records of previous journeys rather than permanent descriptions of the plane.