4th Edition.
Book is in excellent second hand condition.
No realm in the D&D 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. Underdark contains everything a Dungeon Master needs to run adventures or campaigns set in the vast underworld of his or her D&D campaign.