Expedition to Undermountain

"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 blood-maddened minotaur two rests later, then Ironhewer stumbled into a magical portal and vanished screaming. We dared not follow him. It is said thatthese 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."

Summary
Expedition to Undermountain is a combination sourcebook/campaign adventure, for adventurer levels 1-10. The book is split into an Introduction (briefly describing Halaster's death, and a synopsis of the adventure), the first chapter (which briefly describes Undermountain, with maps of most levels and sublevels) , chapters 2-5, which are the campaign adventure, and an appendix of new creatures, such as the Eyeball Swarm, and new items, such as the Crown Adamant.

This is the 3rd ed. supplement for undermountain