From the back of the book...
No one knows what lurks in the depths of the mad archmage's halls... but you're about to find out.
Day, night, I can no longer tell. Gargoyles carried, off the wizard while we were roping our way down Belkram's Fall. Evendur the paladin fell beneath the axe of a Hood-maddened minotaur two rests later, then Ironhewer stumbled into a magical portal and vanished screaming. We dared not follow him. It is said that these halls hide treasure beyond imagining, but even if we found Halaster's hoard in the next chamber, we are so hopelessly lost that I doubt I would live to spend a copper of it.
This Dungeons & Dragons adventure presents the vastest, deepest, most legendary dungeon of them all - Undermountain, the domain of the mad archmage Halaster. Below the streets of the city lie more than twenty levels and sublevels, some miles in extent. Ruined fortresses, secret shrines, subterranean rivers, forgotten crypts, and monsters of every description lurk in the darkness below. This campaign adventure is designed for characters of levels 1-10 and features an easy-to-use combat encounter format. This book also presents new magic items for player characters and an overview of Undermountain as the basis for any D&D campaign.