Undermountain is a vast and complex dungeon located beneath the city of Waterdeep in the Forgotten Realms campaign setting of Dungeons & Dragons. Originally created by the powerful wizard Halaster Blackcloak, it serves as a testing ground for adventurers and a home to various monsters and treasures. The dungeon is known for its ever-changing layout and numerous levels, each filled with unique challenges. Adventurers explore Undermountain in search of fame, fortune, and powerful artifacts. The dungeon is populated by a variety of creatures, including goblins, undead, and magical beings. Many adventurers have entered its depths, but few return, making it a place of both danger and allure in the world of Dungeons & Dragons.