Abyssal realm

The Outer Rifts.

The Abyssal realms are the myriad pocket layers within the Outer Rifts. They have their own gravity, ecology, and denizens, and are obliterated or changed seemingly at random, as the chaotic nature of the Outer Rifts exerts itself. There is no direction, no meaning, and no safe place in the Outer Rifts—a being wandering in from another plane could easily be totally vanished when a rift closes. The Abyssal realms occasionally open as cracks or chasms to the rest of the Outer Sphere, disgorging hordes of demons, or else echoing with a desolate silence.

Anchored realms

Not all realms are so chaotic, however. The home realms of the demon lords seem to be relatively immune to the constant destruction and creation, though they change slightly in every "day" (for the Universe, as each realm can have its own sun or none at all). These anchored realms, or anchor realms, may just be more static than the others, or the demon lords may themselves keep the realm from being overly changed.

There are many realms which are just as solid as those of the demon lords, which often serve as battlefields for demonic armies, whose masters fight against each other to gain more power. Even those that have not already been purposed for combat contain the demonic races, who could have been birthed from the plane itself or migrated there when it formed.

River Styx

The only constant in this always-changing plane is the River Styx, which threads its way through or alongside all of the major layers and whose tributaries are never far from any realm. Though linear movement is nigh-impossible, with the improbable loops and extra-dimensional angles, finding the Styx is the best way to make it out of the rifts.

Notable realms

See also: Category:Abyssal layers

These are the more important realms that a traveler of the Outer Rifts might know:

• Ahvoth-Kor, the jungle realm of Angazhan.
• The Ashen Forge, home of the hryngar deity Droskar
• Basalfeyst, home of the four barghest demigods known as the Goblin Hero-Gods
• The Blood Clefts, current home of the exiled Areshkagal
• Bzuulzeel, the brackish backwater realm of Ghlaunder
• The Cathedral Thelemic, realm of Socothbenoth
• Diovengia, the library realm of Abraxas
• Everglut, the necropolis realm of Kabriri, patron of ghouls
• High M'Vania, home of Pazuzu's aerial court
• Ishiar, underwater realm of Dagon
• Kurnugia, kholo-infested realm of Lamashtu
• The Midnight Isles, dark realm of Nocticula
• Nesh, fog-shrouded realm of Zura, the Vampire Queen
• Pleroma, the false paradise of Abraxas, Master of the Final Incantation
• The Rasping Rifts, the vermin-infested chasms that are the realm of Deskari
• Rift of Repose, hidden and unclaimed it contains the quasi-souls of dead demon lords
• The Sea of Whispering Sands is the home realm of Areshkagal, but has been repossessed by her younger sister Aldinach. It is an immense desert interspersed here and there by ruined cities.
• The Winding Wood of Shivaska, the Chained Maiden

References

Paizo published an article titled "Gazetteer of the Abyss" in The Midnight Isles that provides an overview of all reasonably well-known Abyssal realms.

For additional as-yet unincorporated sources about this subject, see the Meta page.