The buildings of the Smithsonian Institution not only contain impressive collections; they are themselves icons of great cultural significance, many of them part of the historic National Mall. The Smithsonian's unique buildings, shown in A Guide to Smithsonian Architecture, illustrate the changing styles and sensibilities of America as an evolving nation. Representing the work of major architects, each building evokes a specific time in history: the mid-19th-century turreted Castle, the sky-reflecting mid-century modern Air and Space Museum, and the golden, undulating, 21st-century American Indian Museum.