Florence is a lovely city. It's really small and you can walk anywhere - and as you walk, at every corner you might be surprise by great sculptures, buildings or very attractive restaurants. There is an insane amount of art from the Renaissance, and Michelangelo's work is as amazing as you may expect. The food is fantastic and cheap if you compare to big cities. I recommend staying a night to have dinner looking at the Duomo, but you can also enjoy the city making a day trip from nearby cities.