The Smithsonian is my favorite capital destination. Seeing The Declaration of Independence at the National Archives is something that ought to be done, although it is not in the best of shape, it is the founding document of our country, and worth seeing. The memorials to FDR and the veterans of World War II, Korea, and the Vietnam memorial are proximate to each other, and ought to be high on the list. Farther afield, but still very important IMO is the Arlington National Cemetery, inclusive of the Iwo Jima Memorial and the Kennedy gravesite.