Smithsonian National Air and Space Museum

The national air and space museum is a necessary stop for anyone interested in aircraft of space travel. It's got incredible exhibits detailing the history of aviation and space exploration, including real vehicles, replicas, and a moon rock you can touch. This is probably the best collection on the history of air and space travel anywhere.

Steven F. Udvar-Hazy Center

An annex to the National Air and Space Museum located in a massive hangar near Dulles Airport, the Steven F. Udvar-Hazy Center is one of our favorite museums. Make sure to go on a (free) guided tour, offered at minimum at 10:30 am and 1:00 pm but usually more frequently.