Spy MuseumNewseum Hillwood Estate and GardensNational ArboretumNational CathedralNational Geographic MuseumNational Museum of Crime and PunishmentNational Building MuseumFrederick Douglas Museum Adams MorganU Street GeorgetownOld Town AlexandriaNational HarborDC has more to offer than the typical monuments and Smithsonian museums
The Smithsonian museums are African American History and Culture African Art Museum Air and Space Museum Air and Space Museum Udvar-Hazy Center American Art Museum American History Museum American Indian Museum American Indian Museum Heye Center Anacostia Community Museum Arts Industries Building Cooper-Hewitt, National Design Museum Freer Gallery Hirshhorn Museum and Sculpture Garden National Zoo Natural History Museum Portrait Gallery Postal Museum Renwick Gallery Sackler Gallery Smithsonian Institution Building
As a previous answer said, there are hundreds, so it depends on your interests. Here s one list: http://www.frommers.com/destinations/was��
you might want to narrow that down according to your interests...