A nice couple of weeks of downtime in an upscale part of town. Training, spell/magic item research, fun roleplay interactions with "normal" NPCs...and of course, when they're getting comfortable, the unexpected in-town mystery, political intrigue or "monsters in the sewers" adventure, saving the town and securing their reputation as "heroes" in the eyes of the people.
And congrats to your party.
Have fun and happy (urban) adventuring.
--Steel Dragons
Do you mean some adventure in Undermountain? As I remember Undermountain, it was pages of poster maps and supplements.... I didn't think it could be "finished."