"Waterdeep: The Mad Mage's Dungeon" is an exciting adventure for the Dungeons & Dragons role-playing game set in the city of Waterdeep and the famous dungeon known as Undermountain, ruled by the enigmatic Halaster Blackcloak, the Mad Mage. The adventure picks up the story that began in "Waterdeep: Dragon Heist" and takes adventurers from level 5 to level 20 if they decide to explore the entire dungeon. The book details the 23 levels of Undermountain, as well as the underground refuge of Skullport, offering treasures, secrets, and challenges for the intrepid adventurers who venture into this dark and labyrinthine underworld.