From publisher blurb:
Expedition to Undermountain is a 224-page super-adventure that revisits the greatest dungeon in the Forgotten Realms campaign setting. Located beneath the city of Waterdeep, Undermountain has lured countless heroes to their doom.
Like other adventures in the “Expedition” series, this product takes a classic D&D location, updates it for v.3.5, and features many new surprises. It also includes source material for the players and a new combat encounter format designed to make the Dungeon Master’s job easier, as well as information to help Dungeon Masters adapt the adventure to serve their home campaigns.