Through great pain and effort, the Fraternity of Order has cataloged seven hundred and three layers of the Abyss; there are assumed to be many more. The great Codex of the Infinite Planes says there are exactly six hundred and sixty six, but this number is thought to be merely symbolic in some obscure way, probably borrowing images from the bizarre thoughts of one of the many slaves of the book. The Codex mentions many layers that the Guvners can't confirm, and omits many that the Fraternity considers the most significant, sometimes considering them to be part of other layers or even planes and sometimes not describing them at all.

Discovering the exact number, if numbers as such are even applicable in the Demonholme, has been hindered by the discovery of an unknown number of parasitic sub-planes, finite realms attatched to one or more infinite layers and slowly draining them of energy, as well as at least two transitive planes, other than the Astral, in which the Abyssal layers swim.

The layers seem to have no particular structure or pattern in the way they relate to one another metaphysically; the Abyss is commonly depicted as a spiralling pile of layers stacked on top of one another with the Plains of Infinite Portals on top, but this is merely a convenience. Except in the case of a few 'clusters' like Azzagrat, portals between the layers do not suggest any particular affinity or bias toward others said to be 'above' or 'below' them, and in fact the various layers randomly come in and out of convergence, making travel between them more or less difficult at various times.

Some abyssal layers act as the equivalent of inner or transitive planes to others: the 47th layer of the Abyss, where Graz'zt rules, is a Plane of Shadow to the 45th and 46th. Torremor, catalogued as the 503rd Abyssal layer, acts as an elemental plane of air for dozens of nearby domains. Sulfanorum, catalogued as the 303rd, does the same for dozens more. The largest clusters of layers are around the Plain of Infinite Portals, catalogued as the first plane of the Abyss by both the Fraternity of Order and the Infinite Codex, and the Grand Abyss, catalogued as the fifth layer by the Guvners and the 666th by the Codex.

Pazuzu, Torremor's master, is rarely at home. Instead, he flies through many surrounding layers, where the lords are forbidden to harm him by the command of those who even they fear. Pazuzu spends most of his time in the Plain of Infinite Portals, where he seems to be watching for something to come through one of the layer's endless gates. Pazuzu is neither god nor demon, although demons are permitted to act in his name (see the movie, The Exorcist). Instead, Pazuzu seems to be a servant of some kind of certain primal entities who existed before the Abyss was formed. They remain aloof from the politics of the tanar'ri and their ilk, but seem to have schemes of their own.

Two towers spiralling around one another and capped with skull-like minerets mark the Palace of Abysm, Demogorgon's stronghold in the layer known as the Gaping Maw. Close observation by those learned in such things reveals the towers to be twisted versions of the Tower Arcane and Khin-Oin, and in fact Demogorgon has a group of twelve baernaloths imprisoned on one of Abysm's lowest levels, along with two ancient proto-tanar'ri and several unrecognizable things, from which he hopes to wrest important secrets, including the secret of his own origin.

The Olympian Forests of Arborea were once a single layer surrounded by four eidelic elemental realms, as certain layers of the Abyss are today. The great wars surrounding the Godsbirth changed this, causing the Olympian planes of Air and Earth to decay into a single limbic region, Pelion, and the Olympian Plane of Fire to drift into neighboring Ysgard with the retreat of that realm's native giants. Occasionally travelers in Pelion encounter oases, places where the old planes of Air and Earth never completely bled together. These oases resemble whirlwinds or mountains filled with lush vegetation and animal life, similar to Arvandor but with a strong elemental bias.

Numerous misty sub-planes surround Arborea's first and primary layer, inhabited by eladrins who use them for hidden rites of transformation and ascension.

The Dancing Lord is a mighty tulani who frolicks aloof from the court of Lady Morwel. He has his own court, a place of constant movement and energy. More than anything, the Dancing Lord fears being merged with his myriad other selves, scattered throughout the planes.

Hosts of asuras mostly serve gods of chaos on this and neighboring planes. Devas and agathinon serve other gods - rarely can a deity inspire both asuras and aasimon to work together. The main exception is the eladrin queen Morwel, who has an elite group of chaotic celestials who guard her court at all times.

Often asuras will serve a titan; aasimon never will.

Mount Olympus, unlike her smaller sisters Mount Ossa and Mount Pelion, is a plane in its own right ruled by the Hellenistic pantheon and others. It dominates the first layer of Arborea, often called Olympus, and mythical creatures often escape from it into the unending woods.

It's possible that the childlike m'be are more basic to the plane than the eladrins, who cannot be traced before the birth of the titans. Eladrins tend to treat them protectively, like precocious younger siblings. A group of m'be elders hold an honored place in Morwel's court.

Bytopia is a plane divided between several major hierarchies, most of whom willingly cooperate for mutual benefit. Much of Dothion is watched over by archons from Mount Celestia and their aasimon guides. The power of gems and humor, Garl, has his own celestial hierarchy made up of altered archons and devas, with a few planetar aides. Guardinals from Elysium frequent the plane as well, cooperating with the archons in aiding the mortal inhabitants and petitioners and warding off evil. Finally, the air sentinels (thought to be from the elemental plane of Air) watch over the layer of Shurrock with the aid of allied devas. Groups of hollyphants, baku, spirits of the air, air maidens, buraq, and other celestial races also wander about, aiding one faction or another. In Bytopia, it's not uncommon to see groups of radically mixed celestial races, such as eladrins and archons, working together.

One of the most ancient groups of aasimon in the Paradises was originally from Mount Celestia. They went rogue many hundreds of thousands of years ago, abandoning their patron deity and attempting to create more of their kind using a kind of primal celestial mud native to Elysium. They succeeded, but the powers of Elysium drove them back toward their native plane. No longer welcome there, either, they live in a fortress in Bytopia, dreaming hopeless dreams of their own redemption.

There is said to be a mountain in Shurrock that ignores the planar boundary, leading up to the layer's hidden starry sky.

Most of the gods in Mechanus were exiled there by the Powers of Creation, thought to be the predecessors of current powers like Moradin, Tvashtri, Ilsenine, Io-Chronepsis, and the Lady of Pain. Omnipotent moderators keep the gods in Mechanus, and keep them in line.

The Jade Palace of Shang-ti fills a vast gear in which all the high-ups of the Celestial Bureaucracy meet annually to report on the status of its many territories and subject pantheons throughout the planes. It is guarded by inevitables, celestial dragons, and terrible demons, but the fabulous vessels the gods use to travel between planes are visible from hundreds of miles away.