The planes of the and the Outer Sphere form the overarching structure of the multiverse. With their unimaginably ancient histories and vast scales, they contain most of reality within their borders. Yet the dimensions of reality are not static, particularly in the Astral and Ethereal Planes, which serve to connect the other planes. Under the right conditions, any plane can warp so profoundly that portions coalesce into entirely new planes. These self-contained pockets of reality are known as demiplanes.
A typical demiplane is a relatively small, finite plane governed by its own set of laws determined upon its creation. Some of these pocket dimensions owe their existence to the collision of natural forces within other planes. The Positive and Negative Energy Planes exert powerful tidal forces upon the Ethereal Plane, generating ethereal mists. However, these forces are not perfectly synchronized, and when the strain from opposing forces grows too great, the Ethereal Plane sometimes releases energy by coalescing ethereal mists into a demiplane. Occasionally, instead of forming a new demiplane, these mists graft themselves onto an existing demiplane, which expands to accommodate the new material. Meanwhile, in the Astral Plane, the ever-shifting currents of the River of Souls combine with energy from the Maelstrom and the Plane of Fire to produce massive, hurricane-shaped astral storms. Like hurricanes on Golarion, these storms have stable eyes at their centers. When conditions are right, the Astral Plane can release some of a storm’s energy by creating a demiplane in its eye. These demiplanes can grow over time as they absorb storm-tossed fragments of the Astral Plane into their mutable structures. Astral and ethereal demiplanes are similar in structure, though the differences in their creation leave lingering effects. Because of the role of currents on the River of Souls in their creation, astral demiplanes bear fragments of the nature and memories of passing souls. Meanwhile, ethereal demiplanes can absorb echoes of dreams, most commonly from the pull of the Dimension of Dreams, and particularly from dreams tied to strong emotions. In the absence of outside interference, these lingering fragments determine the demiplane’s properties and characteristics.
While some demiplanes arise from planar forces, others are born when individuals deliberately fracture pieces of the Astral or Ethereal Planes and reshape them into pocket dimensions to suit their needs. Even mortals can weave demiplanes into existence with complex rituals or powerful magic. The most common reason behind the creation of demiplanes is a desire to isolate their contents. Demiplanes serve as ideal, protected havens for experiments, as well as for manipulations of time and space that would prove difficult or impossible to produce in other places.
The true definition of a demiplane is a matter of debate. In its most restrictive definition, only self-contained pockets of reality formed from the Astral or Ethereal Planes and accessible via typical methods of planar travel—such as plane shift—qualify. This definition excludes secluded places that the gods have formed by reshaping portions of other planes, such as Desna’s realm of Cynosure, and places that are difficult or impossible to access via standard methods, such as the mythical Akashic Record and Rovagug’s prison, the Dead Vault.
Some demiplanes include the word “Dimension” in their title, as is the case for the Dimension of Dreams and the Dimension of Time. A dimension is a type of demiplane that breaks two of the common rules most demiplanes share. First, a dimension is always a Transitive Plane that overlays all other planes, including other dimensions. Second, a dimension is an infinite space that encompasses all of reality; it is never a small, finite plane. However, some scholars believe that dimensions are not demiplanes at all, and insist that other Transitive Planes like the Astral Plane, the Ethereal Plane, and the Shadow Plane are, in fact, dimensions.
The following pages present a number of the most prominent and best-known demiplanes. A summary of several others appears below.
Book of the Damned: The multiverse’s greatest chronicle of blasphemy, the Book of the Damned, is more than a simple tome. Its holder can enter the demiplane within and wander its chronicles of depravity.
The Circle Between: The Bramble Maiden and her circle of druidic followers watch over this wilderness demiplane, where plants and animals from myriad worlds flourish. The plane’s name comes from a circle of standing stones that hold dozens of extraplanar portals.
Crypt of the Dying Sun: The pale red glow of a dying star illuminates the tomb at this demiplane’s heart. This tomb serves as the lair of an ancient vampire sorcerer named Larynsang the Wasted.
Fleshwarren: This demiplane appears to be entirely encased in a massive corpse. Most travelers who find themselves in the Fleshwarren’s repulsive halls are trapped. The plane blocks most planar travel magic, forcing many visitors to survive off the plane’s flesh. However, those who do so are forever cursed, unable to draw nourishment from any other source.
Freehold of the Rogue Angel: The fallen celestial known only as the Forsaken Martyr rules over this domain. The Martyr plies his visitors with an obsessive series of questions and sometimes offers them treasures in exchange for specific tasks on distant planes.
Immortal Ambulatory: While most gods keep their realms firmly situated on a plane, the dragon god Apsu has created the Immortal Ambulatory, a demiplane that he can pilot freely through the multiverse.
Kakishon: The legendary archwizard Nex compelled proteans to weave the realm of Kakishon from the raw substance of the Maelstrom as a tool for his wars against Geb. The demiplane remained lost for centuries, until the wizard Andrathi discovered it and repurposed it as a prison for his genie enemies.
The Lost: Visitors to this demiplane find themselves adrift in a sea of childhood memories. The immortal children who live here encourage travelers to stay and enjoy themselves, savoring a life free from the burdens of adulthood.
Machine Armory: Thousands of machine soldiers await orders in this mechanical demiplane. The Machine Armory’s most striking feature is its central tower, a massive metallic structure with no apparent entrance that emits the constant whir of turning gears.
Mnemovore: Mnemovore appears as a collection of halls of arcane knowledge, stringing together grand libraries and arcane laboratories from a wide variety of times and cultures. Many of the these places were once independent demiplanes of their own before Mnemovore absorbed them, sating its eternal hunger for arcane knowledge. Nine different factions of outsiders roam its halls, but none of them can remember what happened before they appeared on the demiplane.
Prison of the Laughing Fiend: Tegresin the Laughing Fiend is the lord of this astral demiplane. The story of how Tegresin came to be trapped here changes each time he tells it, but what remains consistent is that a group of powerful warlords summoned him for aid, and, when all was said and done, Tegresin wound up imprisoned here along with the souls of the warlords’ descendants.
Runeforge: Seven runelords of Thassilon constructed Runeforge to serve as a joint magical research facility. Runeforge was the site of great collaboration between the empire’s brightest minds.
Worldscape: The powerful wizard Nex created the Worldscape to aid him in his siege of the city of Absalom. The demiplane draws in and imprisons legendary warriors from Golarion and two other worlds. Its reality-warping powers can lift these champions from the past or future, or even capture alternate versions of them from multiple versions of the same world. During the siege of Absalom, Nex channeled the demiplane’s power to create phantom duplicates of these warriors and force them to aid him in battle.