This annex to the Smithsonian's Air and Space Museum fills a large hangar near Dulles Airport! It features much more of the museum's collection which can't fit in the much smaller space on the national mall. A blast for the engineering-minded!
Georgetown is a particularly charming and architecturally rich neighborhood of DC. It was founded in 1751 (well before Washington itself) and retains an unusually well-preserved historic feel with cobblestone sidewalks, Federal and Victorian architecture, and leafy side streets. It also offers river views, cute shops, and cafes.