Did you know there are actually two Smithsonian Air and Space museum locations? There is one on the National Mall in Washington, DC, and a second in Virginia near Dulles Airport, called the Udvar-Házy Center. The Udvar-Házy location is an enormous hangar filled with historically significant aircrafts, aircraft parts, and spaceflight artifacts, including such highlights as the Enola Gay, an SR-71 Blackbird, and a space shuttle. If you are ever stuck at Dulles Airport and have some time to kill, there is a very cheap ($0.50 each way per person) shuttle between the airport and the museum.
For those unfamiliar with American aircrafts (as I mostly am), the Enola Gay is the plane that dropped the atomic bomb on Hiroshima. The SR-71 blackbird is the fastest plane ever built, even though it was built in the 70s. It flies so fast that at rest, its joints aren’t perfectly sealed, and it can leak fuel. This is because the metal expands significantly due to heat at high speeds. The museum also hold various antique aircrafts, aircraft oddities, engines and engine cross sections. Another area holds retired military planes, and a third area holds NASA artifacts. I went there a couple of years ago. My creative commons folder of images is here, and I include a few pictures below.