[danielf]

I'm a little surprised by #2 (which really doesn't look that impressive to me). I'm also surprised that the pyramids and Angkor didn't make the list. Angkor Wat itself is pretty impressive, but with all the other temples that make up the complex it is without a doubt the most impressive thing (structure wise) I've seen in my life. We spent 5 day there. Four days visiting the main temples, one day to revisit the really special ones, and one day visiting the 'outlying temples'. I'd go back at the drop of a hat.

Some nice photos here