The Old Post Office Pavilion, also known as Old Post Office and Clock Tower, located at the intersection of 12th Street and Pennsylvania Avenue, was constructed between 1892 and 1899 to house both the U.S. Post Office and D.C. Post Office.

Willoughby J. Edbrooke's design, makes its the last major example of Richardsonian Romanesque with its rustication, strong semi-circular arches, and squat clustered columns, united by a foliate Sullivanesque capital-frieze. When completed in 1899, it was the city's largest office building and was first to incorporate a steel frame. The 315-foot-high clocktower is the third tallest structure in Washington D.C.

Today it has been rehabilitated into office and retail space shared by the federal government and private businesses. The expansive interior atrium is now home to shops, federal offices, entertainment space, and a food court.