Astral Sea

A space between everything. If you are ever nowhere in the multiverse, you are in the Astral Plane. This plane isn’t specifically a plane, but rather a nonspatial nonplane as it has no space and planes are specifically spaces. The Astral Plane has been described as a silvery horizon that extends all around you like you are inside a silver orb, to a dark plane with twinkling lights in the distance like stars and stretching out before you is a sea of silvery cloud-like mists.

Geography

The Astral Sea is more of a starscape of purple-black with twinkling lights in the far distance, deep silvery-grey clouds that aren’t liquid or mist, and across the ‘horizontal’ of this plane, those clouds become separated so that ‘below’ are where the denser clouds congregate and above the line are the lighter clouds. Most will orientate themselves so that they travel with the denser clouds beneath them.

Ecosystem

Because there is no gravity or atmosphere in the Astral Plane, objects continue to move. This means that arrows fired from bows, rocks thrown or matter ripped from a plane of existence drifts through the Astral Plane. It's not unheard of for an astral skiff to come under fire from arrows that had been traveling for hundreds of years from an ancient battle site.
But, organic creatures do not exhibit that. In fact, when a creature sleeps on the Astral Plane and they are traveling somewhere, momentum does not keep them moving forward and so they stop where they were until they reawaken and focus on where they wish to go. Non-organic matter is always moving forward because that's what the mind thinks should happen. The Astral Plane is about perception and not actual reality.

Tourism

The Astral Plane is a strange locale for most adventures and, as it is a transitive plane, is rarely used for more than just getting from one location to the next. As the Astral Plane is the location between everything, you can easily travel from one domain to the next using it, and most travelers will never realize they were ever in the Astral Plane. Spells, like Plane Shift, immediately sweep you from your current plane, like the Material Plane, through the Astral Plane and then to your destination, like the Nine Hells or Hestavar.
For travelers in the Astral Plane, and not using it to take you elsewhere, you can find yourself adrift in the vastness of nothing. Depending on the edition, you may only see the silvery-greyness of nothing spanning infinitely all around you. Or you may see silvery clouds forming some sort of horizon that you slowly adjust yourself to with twinkling stars in the distance.
Travelers who find themselves in the Astral Plane are in a strange locale and they should be on constant guard. While there is no atmosphere to speak of and very little to impede your sight, your vision is limited in the Astral Plane. You can only see a few thousand yards out, which means that astral pirates could be just out of range of your vision and heading near your location quickly.
While you are in the Astral Plane though, you needn’t worry about breathing, food or drink. Time behaves strangely on this plane and while you might spend 50 years in the plane, your body will not age until you leave it. For an outsider, this plane is unlike any you might be traveling too, and it may be a plane you will never leave for fearsome creatures roam the nothingness.

Type

Plane of Existence

Location under

The Great Wheel