One of the nicest aerospace museums in the United States is the Museum of Flight, outside Seattle, Washington. The professionally-displayed collection of more than 150 aircraft is impressive both in size and quality. From a 1914-era Caproni Ca.20 fighter to an Aérospatiale-BAC Concorde supersonic airliner, there are aircraft of all shapes and sizes. The spacecraft collection has some notable items as well, from the enormous Space Shuttle Full Fuselage Trainer, to a 1970's era Viking Mars lander and orbiter. It is the Viking lander which drew me cross-country for a recent visit.
Before Viking, little was known about the surface of Mars; no spacecraft had successfully landed. During six years of surface operation (1976-1982) the Viking 1 and 2 landers revealed the cold and dry surface in thousands of photographs, while science instruments analyzed soil chemistry and atmospheric composition and pressure. The museum's lander is the backup unit constructed by Martin Marietta alongside the two primary units (which, of course, are now on Mars). Due to project funding limitations, this backup lander was not completed. Although the lander thus looks rather spartan, I find it a boon to study. The structure is almost entirely exposed to view, rather than concealed behind insulation blankets, covers, and exterior components. Part of the lander interior is even visible through open access panels.
My Web album contains many more detailed photographs of this Viking lander "Flight Capsule 3". And don't forget to view the Museum of Flight website!