Dungeons & Dragons - Waterdeep - Dungeon of the Mad Cave HcDelve deeper than you ever thought possible in this adventure for the world's greatest roleplaying game! Hundreds of years ago, long before Waterdeep had been built, Halaster Blackcloak carved a vast dungeon beneath Mount Waterdeep, stocking it with all manner of creatures from across the planes. Over time, Halaster has gone quite insane, and the dungeon he carved, now dubbed "Undermountain", is a labyrinthine death trap for those bold enough to