Arborea, meaning 'land of trees', is the plane of Chaotic Good in the AD&D Planescape setting. Of all the Outer Planes, it is the most emotional and passionate. It has three layers:

Olympus/Arvandor: These names, actually of the homes of the Greek and Elvish pantheons, have been used as names for the whole plane. This layer has a Mediterranean climate and is very beautiful.
Ossa/Aquallor: This layer is the home of Poseidon, and of his elvish counterpart, Deep Sashelas.
Pelion/Mithardir: This layer is a desert, nearly empty. The elvish name means 'white dust'.

The human names of these layers are the names of three great mountains in Greek mythology.