Exterior of the Washington City Post Office Building, by Penland, Dane A, 1992, Smithsonian Archives - History Div, Exterior of the Washington City Post Office Building, designed in 1914 by Daniel Burnham, located at North Capitol and Massachusetts Avenue. A portion of the lower level of the palatial beaux arts quarters of the Old City Post Office Building became the new home for the National Postal Museum. Opened in 1993, the museum was established in 1990 under an agreement between the Smithsonian Institution and the United States Postal Service..