RECOMMENDED: 50 best New York attractions
Technically, the U.N. complex is international territory, but that doesn’t mean you get immunity when you enter (so don’t steal from the Delegates Dining Room buffet). The striking, 39-story Secretariat Building (designed by Brazilian architect Oscar Niemeyer) is the complex’s most eye-catching structure, but it’s not open to the public. Visitors can instead tour the midcentury assembly room whenever dignitaries aren’t using it, or enjoy free art in the lobby. The U.N. even has its own post office, but the personalized stamps sold there are only good if mailed from that spot.