Ann T.
Yelp
Personally, I really loved Piazza del Duomo, with its beautiful baptistery, cathedral and its infamous tower. The baptistery is a beautiful, circular building that, like most Italian architecture, is extremely ornate. I keep using that word to describe architecture and art in Italy - but it's true! The baptistery is also remarkably well-preserved. The exterior reminds me a little bit of the Duomo in Milan. The interior is nice but there isn't very much to look at. You can climb up to a second level and get an overall view of the interior of the baptistery which is cool. Now, once you get up there - DO make sure to look out the windows. You'll find the perfect place to snap a picture of the cathedral!
My suggestion would be to visit around 4-5pm as there seem to be a lot less people wandering about and you can get the obligatory tourist shot of yourself holding up the tower, without a bunch of strangers in your pics!