The Medici's immense 16th-century palace across the Arno, now housing five museums including the Palatine Gallery — a series of lavishly frescoed rooms crammed with Raphael, Titian, and Rubens. The Boboli Gardens stretching behind the palace are formal Italian gardens on a monumental scale, with fountains, grottoes, cypresses, and long views over the Florentine hills.
Pair the two on an Oltrarno afternoon: an hour in the Palatine Gallery, then an hour in the gardens. Less crowded than the Uffizi and worth it for the setting alone.