Mishtar

Mishtar is the world tree. The word Mishtar is synonymous with creation, everything brought forth by Good, directly or indirectly.

Good created Mishtar then created the celestials to tend to it. The celestial Evil rebelled, saying Mishtar should never have been created. He and his followers, the fiends, claimed the highest branches of Mishtar as their home, but were unable to destroy Mishtar or stop it from growing, since Good and the celestials control the root.

In the center of Mishtar (the top of the trunk) sits Rojopotis, the prime material plane. Rojopotis is surrounded by the Ethereal Sea, which connects all material planes, including the elemental planes which form it's outer coast. On the other edge of the elemental planes lies the Astral Sea, which connects the physical world to the spiritual. No living mortal can pass beyond the outer edge of the Astral Sea. On the outer edge lie the heavens, domains built by gods to house the souls of their followers after death. Opposite the heavens, also on the edge of the Astral Sea, lie the Abyss and the Nine Hells. Beyond the heavens and hells lie the Outer Planes, home to celestials and fiends.