Planes outside the World
It is widely accepted that there are other dimensions parallel to the actual material world. Wizards have known this for a long time, and both wizards and clerics derive much of their power from other planes’ energy.
The planes that are known to exist are the Material Plane, the Feywild, the Underdark, the Astral Plane, and the Infernal Plane.
Magic comes from the Feywild and the Underdark, while clerical abilities come from the Astral and Infernal planes.
The Feywild is rumored to be an odd place, full of fantastical beings and strange creatures.
The Underdark is rumored to be terribly dark and full of horrible beings. Many believe that the inhabitants of the Underdark have only malicious intent towards humans.
The Astral Plane is home to the gods, and is supposed to be all aglitter.
The Infernal plane is home to demons and devils, and is rumored to be filled with fire.
Some believe there are other planes than these, but no proof has been found.