The National Portrait Gallery and the Smithsonian American Art Museum share a magnificent Greek Revival building in Penn Quarter, one of the most handsome federal buildings in Washington. Both are free and together they make an excellent half-day.
The Portrait Gallery holds portraits of every US president, from Gilbert Stuart's famous unfinished painting of Washington to Barack Obama's striking Kehinde Wiley commission. The American Art Museum specialises in work by American artists from the colonial period to the present, with particular strengths in folk art, New Deal murals, and contemporary work. The central atrium — the Kogod Courtyard, now roofed in glass — is one of Washington's best indoor spaces and serves as a cafe.