The Ruins of Undermountain II: The Deep Levels

From the Back of the Box:

The legacy of the most infamous super-dungeon of all time continues in this unspeakably huge and darkly fun boxed set. The first set was just the beginning - now, submit your heroes to the Deep Levels! You get: 2 entire books of monsters, adventures, adversaries and treasures, 16 pages of new monsters, 4 giant poster maps highlighting the most dangerous levels in the dungeon, and a pile of cardsheets to help you whip up diabolical traps in an instant.