The Duomo of Florence is an amazing cathedral. Built over 6 centuries, you can see just about every type of architecture if you know what you're looking for. The exterior is just amazing, with marble of various colors completely covering it. This was put on as late as the 19th century. We attended Christmas Eve mass here, and the interior is very simple. We used this as a landmark to keep us from getting lost. If we could find the Duomo we could find our hotel.