I thought the Sistine Chapel was glorious. Yes, it's crowded, but you get lost in yourself looking up to the ceiling so you don't even know who is around you. Pisa's tower was also a great experience. I was able to take my parents to see Rome, Florence, Venice, Barcelona, and Mallorca, and they still talk about climbing the tower. Lastly, riding a gongola in Venice will always be something I remember. The music echos in the narrow passageways, you see Venice at night in a relaxing way away from crowds, and with the right person it's better than anything you see in the movies.