The Underdark is a fictional setting which has appeared in Dungeons & Dragons role-playing campaigns and Dungeons & Dragons-based fiction books, including the Legend of Drizzt series by R. A. Salvatore. It is described as a vast subterranean network of interconnected caverns and tunnels, stretching beneath entire continents and forming an underworld for surface settings. Polygon called it "one of D&D's most well-known realms".
