Planescape
Planescape is an official D&D campaign setting first introduced in Second Edition. The setting centers around exploring an original multiverse cosmology.
Planescape cosmology
Sigil
Sigil is a city built on the inside of a torus (imagine a tire laying on its side with buildings all around the inside of it). From anywhere on the Outlands (the most neutral of the Outer Planes), Sigil can be seen floating above the great stone Spire, but since the Spire is infinitely high, the only way in or out is through the portals that manifest themselves inside of doorways, windows, and any other kind of bounded space. Because of this, Sigil is also called 'The Cage'.
Portals like those in Sigil exist all over the multiverse, linking distant planes to each other, but the concentration is highest in the Cage. This phenomenon makes Sigil one of the most coveted locations in the multiverse. Gods and fiends would love to take over, but Sigil is guarded by a being called the Lady of Pain, whose diligence bars would-be conquerers from entering the city.
Prior to the events of the Faction War adventure, Sigil's political and philosophical system is dominated by fifteen factions, all vying for the most believers (see Factions, below).
Inner Planes
The Elemental Planes (air, earth, fire, and water) are the most famous Inner Planes, but there are many other planes traditionally grouped into this category. These planes are:
- The Positive and Negative Energy Planes (realms of pure "healing" energy and the force that powers undead, respectively).
- The Paraelemental planes (such as Magma, the intersection of Fire and Earth, or Ice, the intersection of Water and Air).
- The Quasielemental Planes, formed from the interactions of the Positive or Negative Energy Planes and the planes of Fire, Water, Air, and Earth (such as Vacuum, formed from Air and Negative Energy, or Mineral, formed from Earth and Positive Energy).
Outer Planes
There are seventeen Outer Planes, each formed from the moral and ethical alignments of the sentient beings in the multiverse. Most of the Outer Planes are divided into layers; the majority of portals deposit beings on the first layer of the plane. Many of the gods (or 'Powers') in the multiverse reside on the Outer Planes, in lands called realms that are under their direct control. Worshippers of these powers The Outer Planes are:
- The Abyss (chaotic evil). The Abyss has an infinite number of layers, each one unique and filled with hateful, unthinking evil. The tanar'ri (or demons, as they are known on the Prime Material Plane) dwell here.
- Acheron (Lawful Neutral Evil). This is where the souls of those killed in senseless wars go, to fight among the armies of slain soldiers until they are killed a second time and merge with the plane. The first layer of Acheron is the most famous- an infinite realm of gigantic iron cubes, floating in the void, on which vast armies clash. The cubes occasionally collide, smashing anything caught bewtween them to paste.
- Arborea (Chaotic Good). This is the plane of the elven and Greek powers. It is typified by vast rugged geography, immense forests, mountains that peak above the clouds, and other splendors of nature.
- Arcadia (Lawful Neutral Good). Arcadia is a plane of law first and good second.
