The cream of Washington DC's remarkable panoply of historical artefacts and fine art works comes under the general auspices of the Smithsonian Institution, which holds the US national collections of everything under the sun. Endowed by an Englishman – James Smithson, bastard son of the first Duke of Northumberland, who never even visited the US – the Smithsonian was established in 1846 "for the increase and diffusion of Knowledge". This broad brief is reflected in its impressive range of research centers and museums. Nine line up along the Mall, four more are located just north, and the zoo is a few miles north beyond Rock Creek.

The original home of the Smithsonian, the 1849 Norman-style Smithsonian Institution Building, known as The Castle, stands on the Mall halfway between the Capitol and the Washington Monument. It was at first devoted to scientific research, but as the Smithsonian became more of a museum, the sheer accumulation of items necessitated the construction of the various other buildings along the Mall. The old Castle is now the Smithsonian headquarters and main visitor center, 1000 Jefferson Drive SW (daily 9am–5.30pm; 202/357-2700), with the latest details on all the galleries available from the high-tech information desk. The ornate tomb of James Smithson is in an alcove just off the Mall entrance, and the lovely flower-filled Enid A Haupt Garden (summer daily 7am–8pm; winter 7am–6pm) fronts the Castle on the south side. To get a feel for the days when the Smithsonian was known as "the nation's attic", take a look in the adjacent Arts and Industries Building, DC's first "National Museum", which once displayed the hundreds of objects sent here for safekeeping after the 1876 Centennial Exhibition in Philadelphia. A permanent exhibition recounts those days, while other changing exhibits concentrate on African-American and Native American cultures.