No realm in the Dungeons & Dragons world stirs the imagination like the Underdark. This vast subterranean domain holds thousands of adventure possibilities and myriad threats, including drow, mind flayers, dragons, and worse! Entire campaigns can unfold in its depths, and its rewards are boundless. Descend into the depths of the Underdark with this supplement packed with everything a Dungeon Master needs to run adventures set in the vast underworld, including new monsters and hazards, read-to-play encounters, monster lairs, and detailed information on various dark-dwelling 'movers and shakers.'