The world is composed of three demi-planes and seven planes of existence.
The demi-planes are directly connected with the overworld, and are charaterized by not having a physical fixed barrier, but rather some rough boundaries where a individual will gradually enter the demi-plane the further it ventures through.
The planes aren't directly connected to the overworld, but are rather influenced by it. They're not characterized by any physical aspects of the world, but rather by philosophical and methaphysical concepts. All planes share a overplane, where smaller planes are placed in, like islands in an ocean.