Mistwell
Crusty Old Meatwad (he/him)
Sunless Citadel is the classic 3e adventure.
I don't know for sure if there is a 4e adventure that meets the same level of "iconicness" but wasn't there something in the core books; a mini adventure, at least, that probably most people would have tried out?
Agreed. Sunless Citadel or the follow-up Forge of Fury are the best 3e adventures in my opinion.