Undermountain: The Lost Level

The "first official Dungeon Crawl adventure module", it was followed by Undermountain: Maddgoth's Castle, Undermountain: Stardock, and Skullport.

"This Dungeon Crawl adventure includes 32 pages of combat and role-playing hearkening back to classic AD&D dungeons of old. This is a stand-alone module and does not require additional support materials. It can easily be inserted into a campaign on any world, but best fits an Undermountain or Waterdeep campaign within the Realms."