The National Air and Space Museum is one of the Smithsonian museums in Washington, DC, and has a secondary location in Chantilly, Virginia. Its focus is on the development of aeronautics and eventually space travel. It's located at the intersections of Independence Avenue and 4th Street SW in Washington and at 14390 Air and Space Museum Parkway in Chantilly.
Originally, the National Air Museum was founded by act of Congress on August 12, 1946. By this point, there was already a collection of aerospace artifacts possessed by the Smithsonian including Chinese kites and the Stringfellow Engine, some dating back to the 1876 Centennial Exposition. These were incorporated into the new museum, which was a new bureau of the Smithsonian Institution. The development towards spacecraft throughout the 1950s and 1960s sparked the public interest and, on the 1st of July in 1976, the NAM was renamed to the National Air and Space Museum and opened to the public after five years of construction.
Over the years, the museum has acquired a number of famous craft, including the Spirit of Saint Louis, the Enola Gay, a Wright Brothers flyer, and the command module from Apollo 11. Most of these are either suspended from the ceilings of the museum (presumably in midflight) or behind a small glass wall. It's quite a treat to be able to see all of these famous craft in real life.
The Museum has constantly-changing exhibits — ranging from an exploration of how the Wright Brothers designed their flyers all the way up to exhibits and Star Wars and Star Trek — in 22 different galleries. It also has a planetarium, a flight simulator, and an IMAX theater. These are complemented by tours and (of course) a cafeteria and gift shop. A normal day for the Museum will see a huge number of visitors. It's advisable to plan your visit such that it won't be during the average school day or peak tourist seasons for the area, as the constant pitter-patter of little feet (as well as the hormone-addled screaming of twelve-year-olds) does not help one who wants to be engaged in quiet reflection on the majesty of human progress.
The Museum does not solely exist as a source of tours and exhibitions for the public. It also serves to restore and document all of the vehicles that it receives. At the Paul E. Garber Facility in Suitland, Maryland (no longer open to the public), the Museum has over thirty buildings designed to store and provide access to the craft within the collection. Although the vast majority of the Museum's holdings are here, they are actively being moved to the Steven Udvar-Hazy Center in Virginia, which was recently (opened in 2003) built to take over this purpose. It is here that engineers, historians, and other employees of the Museum will work to respectively refurbish and archive information about the vehicles, including ranging from old aircraft to World War II-era bombers and fighters to the Space Shuttle Enterprise. Their work can be requested from the Museum for those who need it. This also includes a simply staggering collection of materials relating to aerospace, including (from the website) "approximately 10,000 cubic feet of material including an estimated 1.7 million photographs, 700,000 feet of motion picture film, and 2 million technical drawings."
Admission is free, although it can sometimes be troublesome to find parking, and tickets to special showings or the planetarium do cost extra. The Washington location is very centrally located, and is easily accessible from the Metro subway system. The Virginia location has a parking lot, at which costs $12 per day to park. A shuttle bus does run between the two locations on a regular basis.
The National Air and Space Museum is an interesting and engaging place to explore. If you're in the area and tiring of all of the art museums, consider visiting. There's something for just about everybody here, as there is enough to see that one cannot experience the entirety within a day.
Source: the Museum's website at http://www.nasm.si.edu