I don't think any place in Florence gives one the sense of peace and quiet in the midst of the tourist mobs quite like Brunelleschi's Pazzi Chapel.
The cloister and refectory along with the Chapel adjoin the church of Sta. Croce,
and are a little island of peace that I have to visit every time I go to Florence.
It is one of the few places where you can usually get away from the crowds.