Chapultepec Castle is an absolute must see in Mexico City! I would go as far as to call it the Versailles of Mexico. The castle was actually used in filming one of my favorite movies Romeo + Juliet. It is located on top of a hill inside Chapultepec Park with gorgeous panoramic views of the city. It is a small hike to reach the top, but nothing strenuous if you are in shape. I recommend getting there early as to avoid the tourists. I got there around 9:45am on a weekday and when I left an hour later it was just starting to get busy. Do not leave Mexico City without a visit here!