The Astral Sea
The Astral Plane can be reached from almost any point in a Prime Material Plane or first layer of any Outer Plane by spell, psionic ability, or alchemical device. It is a barren place of other-dimensional nothingness extending in all directions. What little solid substance that floats in the bright, gray void are typically chunks of matter broken off from their original plane. The Astral has no gravity, but objects do retain their mass.
Time in the Astral flows at the same rate as on a Prime Material Plane, but the effects of time are slowed almost to a stop, and the perception of time in the Astral is greatly distorted―a thousand years in the Astral Plane feels like only a day to the traveler. Creatures do not go hungry or age while in the Astral Plane. For that reason, its mortal inhabitants need to return to the Material Plane in order to have children or to reach adulthood.
On this plane of thought, the existence of true natives was doubtful. The githyanki, however, had been a dominating presence for long ages, ruling from their great city of Tu'narath - but mostly spread about innumerable astral fortresses.