Arborea

Arborea is one of the Outer Planes of the Planescape. Arborea is comprised of three individual layers which physically sit one over another.

Arvandor
The uppermost layer of Arborea, Arvandor is a layer of wide open plains and meadows, with a range of mountains off in the distance from the portal that opens to Sigil. The plane is populated by Pegasi, Chimerae, Gorgons, and other fantastical creatures. The layer has an edge, a sheer drop off that leads straight down to Aquallor.

Aquallor
Aquallor is a vast ocean plane. The waters of Aquallor aren't very deep over most of its surface, averaging roughly 3 feet over most of the plane. There are occasional crevasses that lead deep underwater, where the residents of Aquallor dwell. Coral-themed civilization exists, but have yet to be explored by the party. At the edge of Aquallor, water spills out and down to the depths of Mithardir.

Mithardir
Mithardir, the final layer of Arborea, is an expanse of white sand dunes. The skies are dark as dusk, but the area is still lit to be visible even by creatures without Darkvision.