Smithsonian Institution Building

The Smithsonian Institution Building, located near the National Mall in Washington, D.C. behind the National Museum of African Art and the Sackler Gallery, houses the Smithsonian Institution's administrative offices and information center. The building is constructed of Seneca red sandstone in the faux Norman style and is nicknamed The Castle. It was completed in 1855 and designated a National Historic Landmark in 1965.
The Castle was the first Smithsonian building, designed by architect James Renwick, Jr., whose other works include St. Patrick's Cathedral in New York City and the Smithsonian's Renwick Gallery, also in Washington D.C. The building committee held a nationwide design competition in 1846 and selected Renwick's design by a unanimous vote. A cardboard model of Renwick's winning design survives and is on display in the Castle. Renwick was assisted by Robert Mills, particularly in the internal arrangement of the building.

Wikipedia