Astral plane

It is the space between everything. It is the road that goes everywhere. It is where you are when you aren't anywhere else.

- Naardic of the astral sea   The Astral could be reached from almost any point in a Prime Material plane or first layer of any Outer plane by spell, psionic ability, or device. It was described as a barren place of other-dimensional nothingness extending in all directions. What little solid substance that floated in the bright, gray void was typically chunks of matter broken off from their original plane. The Astral had no gravity but objects did retain their mass so you could throw small items or push off from large objects to move in the weightless environment.  

Time flows differently here

Time in the Astral flowed at the same rate on a Prime Material plane but the effects of time were slowed almost to a stop―a thousand years in the Astral plane felt like only a day to the traveler. Creatures did not go hungry or age while in the Astral plane. For that reason, its mortal inhabitants needed to return to the Material Plane in order to have children or to reach adulthood.  

Geographical Features

Upon entering the Astral plane, travelers saw a silvery color pool nearby—a portal to the location on the Prime Material plane from which they originated. Astral projecting travelers saw their silver cord leading back to this pool. Color pools appeared as two-dimensional circles about 10‒60 ft (3‒18 m) in diameter and only visible from one side unless they had some way to detect invisible objects. Pools of different colors were portals to the different Outer planes. Each Outer plane had its own unique color, but the traveler's home portal was always a metallic silver, rippling like mercury in a pan. Color pools could be used to view the destination plane before stepping through by mentally concentrating on the nearby pool until it became transparent. A viewer could also move (with some limitations) the portal's viewpoint by concentration. Astral projecting travelers formed a new physical body (with silver cord attached) when they stepped through a color pool to their destination plane. The new body was formed out of local materials so the greater the similarity between one's home plane and the destination, the more one's new body looked like the original one.[