The Duomo di Milano, Milan, Italy

A breathtaking stalwart of the Milan skyline, the Duomo’s history spans more than six centuries of worship. The cathedral’s construction began back in 1386 at the peak of Gothic design, but was not truly completed until the mid-20th century. Over the decades, a succession of Italy's greatest architects, engineers and artists worked on the magnificent structure. Even Leonardo Da Vinci sketched some designs for a proposed domed tower, though they never made it off his drawing board.