"Below the city of Waterdeep, through a gaping pit in the Yawning Portal tavern, lies the Undermountain - the domain of the mad wizard Halaster Blackcloak. Picking up after the events of Waterdeep: Dragon Heist, take your characters of fifth level or higher up to level 20 as they explore the entirety of Halaster's home: 23 levels of Undermountain, full of treasure and secrets!"