From publisher blurb:
Introducing Drop-In Dungeons! This series of releases will feature small adventures and dungeons, generally 5 pages or less, that are effortlessly inserted into almost any campaign for the times your players zig instead of zag, and you find yourself unprepared. With the loose and opened ended way Drop-In Dungeons are written, you (the GM) can bait the hook however you want; the appetizers and desssert are up to you, herein you'll find the meat and potatoes.
The Forgotten Halls: No one can remember when the place was built, who built it, or why. But, there is no question that the “Forgotten Halls” are a place of legend among the locals. Most who have gone to explore the halls never returned, though the few fortunate souls who did were able to live comfortably from their plunder for many years.