Great Wheel

The Great Wheel is a popular model of the cosmos.

According to the Great Wheel model, all material worlds exist in the Prime Material Plane. Each is encased in a crystal sphere, which are separated by an ocean or "outer space" of phlogiston. Connected to the Prime Material Plane by the ethereal plane are the Inner Planes: the worlds of raw elemental matter. Finally, connected to the Prime Material Plane by the astral plane are the Outer Planes: metaphysical planes of spirit and mind.