Hollow World is a world campaign supplement written specifically for Dungeons & Dragons. This detailed campaign module proposes that within the sphere of the "Known World" is another world called the Hollow World, a sub-setting for the Mystara campaign world. Hollow World acts as a living "cultural museum" for the planet, forever preserving cultures and races that are near extinction on the surface world. This box set includes the following: A 128-page softbound Dungeon Master's Sourcebook A 64-page softbound Player's Guide book A 32-page softbound Adventure Book Four single-sided poster maps The books include information about new monsters, elves, dwarves, character classes, pirates, and immortals.