Smithsonian Institution

Not one museum but a whole constellation — the world's largest museum, education, and research complex, founded in 1846 from the bequest of the Englishman James Smithson, who never once set foot in America. Its buildings effectively turn Washington into a single, city-sized museum, most of them free, radiating out from the red-sandstone Castle on the Mall. Its own passport booklet is the fun way to work through them.