There have been many things to see in Florence, but one of the most impressive is the Duomo of the Basilica di Santa Maria designed by Brunelleschi and completed in 1436. It looms above the city and can be seen from almost anywhere. So logically, the top of the Dome has the best views of the city. After walking around the exterior and looking inside the church itself I bought a ticket that allowed me to climb the stairs to the top of the Dome.
The top of the Dome was breathtaking and possibly the best thing I've done in Italy so far. The weather was perfect and I had an incredible view of all of Florence and the Tuscan countryside. The stairs to the top of the Dome also allow visitors to walk along a path inside the Dome that runs alongside the fresco painted by Vasari in 1572 titled "The Last Judgement." An amazing painting. I've included some awesome photos I took from the Dome over Florence, although a picture hardly does the view justice.