Guggenheim Museum, Bilbao, Spain
Considered one of the most architecturally innovative and important buildings of the 20th century, Frank Gehry's Guggenheim Museum Bilbao stunned the world when it opened in 1997.
The behemoth, curving structure is composed of titanium, glass and limestone. It was designed to blend into its location alongside Bilbao's Nervion River. Its curves, according the Gehry, were intended to appear random.
The building's 256,000 square feet of exhibit space features art spanning the mid-20th century through the present, as well as ever-changing special exhibitions.