Smithsonian Institution Building
The Smithsonian Castle, located on the National Mall in Washington DC houses the Smithsonian Institution's administrative offices and information center. The building is constructed of red Seneca sandstone in the faux Norman style and is appropriately nicknamed The Castle.
The Smithsonian is mentioned in Dan Brown's latest thriller The Lost Symbol, which takes place in Washington, (yes, I am a Dan Brown fan!) and here's a nice page about facts or fiction in the book!