Many Planescape adventures take place on the Great Wheel, the Inner Planes, and the transitive planes between them. While infinite in extent, and containing similarly infinite possible demiplanes, this overlooks one of the possible attractions of the setting: the chance to adventure between one Prime and another, across a variety of interesting material worlds, some of them inhabited by their own unique and colorful cultures. Spelljammer does this in its own way, but there is, after all, plenty of opportunity for a Planescape game to walk the many Earths.
This thread is for descriptions of Prime worlds to be used as source material for adventures, backgrounds for characters, and the like. Feel free to add your own homebrew world(s), though please be considerate of users who would like to browse: capsule information should come first, and descriptions should, while evocative, be no more than a few paragraphs in length. If you have a lot of material or illustrations for your world, please feel free to provide a link to a web resource for it.
A blank template is below for people to copy and use, followed by an example.
Name: any known names of the world, given by the inhabitants or nicknamed by explorers.
Access: the portal from Sigil if one is known, along with its key(s) and any information such as whether access is controlled by someone. Mention that no Sigil portal is known if this is the case. Any other access information, such as commonly known spelljamming coordinates, portals from other locations, or a caster who knows the appropriate plane shift spell. Known exit routes, if access is not two-way.
Prevailing conditions: Immediate survivability requirements, environmental threats, and any planar traits of interest.
Inhabitants: Any intelligent inhabitants -- just species and density -- and the major ecology in the usual region of arrival.
Description: The longer spiel goes here. A few paragraphs on points of interest in the plane, such as why anyone would come, major geographic features of interest, more detail on any local intelligent cultures, any notable NPCs, and so on. Local adventure possibilities are highly encouraged.