D&D 30 Day Challenge - Day 12 - favorite dungeon type/location

I'm sure I won't be the only one to say this but the Underdark is probably my favorite, the adventure with the boxed set was so thrilling, (I ran it once).  If I remember correctly you could either start off as a member of a Drow family or as an outsider, I picked the outsider path just for the tour to Menzoberranzan, which is extremely detailed in the box.  I suppose if I had to pick a second dungeon location it would be a toss up between the "Caves of Chaos" and any Castle type crawl.

Here's a link to the geography of the Underdark I found
http://www.realmshelps.net/faerun/underdark/pix/undermap.jpg