While Britain is renowned for massive castles where the queen and other royalty reside in style, Washington also boasts its own architectural gems. Among them is the Smithsonian Institution Building, which dates to the mid-1800s. Nicknamed what else? "The Castle, the structure was erected in Gothic Revival style, designed to evoke the Collegiate Gothic in England and the concept of wisdom and knowledge. And like every castle should, it boasts towers, including one that rises 91 feet.