The Underdark Holds Many Secrets A series of earthquakes and eruptions have rocked a normally placid land. Strange creatures sighted in the dark of night raise fears across the already disturbed countryside. As tales of a lost race that once warred with the drow begin to surface, only the boldest adventurers dare to descend into the shadow darkness. Deep Horizon is a stand-alone adventure for the Dungeons & Dragons game. Designed to challenge 13th-level D&D characters, it presents a long-forgotten civilization for heroes to discover and save, if they can. To use this accessory, a Dungeon Master also needs the Player's Handbook, the Dungeon Master's Guide, and the Monster Manual.