The Astral Sea

A shining, silvery-blue void of endless nothing, The Astral Sea, known by academics as the Astral Ring, is a transitory space of subjective gravitic influence that sits outside The Ring of Elements and borders The Unmaking Never. Movement within the plane is in direct correlation with a planar traveler's intellect, and no air is needed to survive by creatures that breath such a thing.
There are few denizens of this infinite expanse, but the Astral Sea's proximity to the Unmaking Never means that creatures in this void are strange in appearance, alien in thought, and extremely dangerous. Tales speak of creatures larger than cities swimming through the void as if it were an ocean (hence the name), and strange-angled, ever-shifting forms that are clearly fighting reality itself to exist.
The most common, albeit still extremely rare, way for an individual to reach this plane is by means of astral projection, whereby they are tethered by powerful magic to a silver cord and dropped into the plane in an ethereal state. Actually making it to the plane via plane shift or other such magics is far harder, as travel here is only possible from the Ring of Elements, The Animatic Plane, The Mortalic Plane, or the Unmaking Never.
Creatures finding themselves marooned in this plane have little recourse but to swim or wait, and must hope for a shimmering, prismatic portal to fly along and scoop them up. Once so collected, the unlucky creature must hope that the portal dumps them in a random plane hospitable to their constitution. These portals, called slipgates, seem to defy the ordering of the planes, as they are capable of providing one-way travel from the Astral Ring to any other plane. Attempts to harness this power have been met with few successes but many vanished planar scholars.