If you find yourself flying through D.C. with a layover at Dulles Airport of 2 hours or more, you can take a shuttle over to the Steven F. Udvar-Hazy Center. Located on the Dulles grounds, it is another branch of the National Air and Space Museum of the Smithsonian. Among the exhibits there is the US Space Shuttle Enterprise, and all the satellite, spacecraft, and aircraft displays you would expect. But there are a few other SciFi goodies as well, including the most complete classic ray gun collection I have ever seen, a small assortment of Robots, a phone booth in the shape of a Mercury capsule, and an R2-D2 USPS mailbox.