Once used to store currency, this is the largest Greek Revival edifice in Washington. Robert Mills, the architect responsible for the Washington Monument and the Patent Office (now the Smithsonian American Art Museum), designed the grand colonnade that stretches down 15th Street. After the death of President Lincoln, the Andrew Johnson Suite was used as the executive office by the new president while Mrs. Lincoln moved out of the White House. Other vestiges of the building's earlier days are the two-story marble Cash Room and the gilded west dome. One-hour tours arranged through your congressperson are available most Saturdays at 9, 9:45, 10:30, and 11:15; participants must be U.S. citizens or legal residents.