Colosseum in Rome. This is the place where I honest realized I was in a foreign country. The Colosseum is larger than life in my mind, but is almost small in comparison in person. It's absolutely beautiful up close, though.
Michelangelo, Sistine Chapel, Vatican this shows both the ceiling and the last judgment. The ceiling is a beautiful work of art with great detail. The last judgement even has more detail and it was done 29 years after the ceiling.