23x Postcard Of The Smithsonian Institution Building The red sandstone Smithsonian Institution Building, with its light crenelated towers, symbolizes the entire Institution to many visitors. Popularly known as the "Castle " this building housed all the Smithsonian's operations when it opened in 1849. Today, it houses the Smithsonian Information Center. Administrative offices occupy the rest of the building. 2005 Smithsonian Institution Postcard size 4 x 6