Astral Plane

The Astral Sea is a dimension outside of the Material Plane.

Lady Allura told Vox Machina during a conversation on how to dispose of the Horn of Orcus they had acquired that, when a Bag of Holding is destroyed, its contents jettison into the Astral Sea.

Creatures
Many beings reside within the Astral Sea, although it is unknown what beings besides the one Lady Allura specifically mentioned.
 * Githyanki