The Duomo, although wonderful to look at, had a very long line to get in so we just took pictures from the outside and kept walking. Florence is a severe tourist destination.
We went and looked at the Tempio Maggiore Israelitico Synagogue but did not go in.
Basilica of Santa Croce and saw the tombs of Michelangelo, Galileo, Machiavelli...pretty amazing, really. The Basilica has a Star of David at the top. Odd.