The octagonal baptistery facing the cathedral, built in the 13th century on the site of a former pagan temple. The exterior is striped in white and green marble on one side only — the project ran out of money before the other faces could be completed, leaving the back walls in plain stone.
Inside, the focal point is the octagonal font of 1502 by Andrea Sansovino, a small but beautifully carved early Renaissance piece. The interior is otherwise plain, almost monastic in feel, and worth a quiet five minutes after the cathedral.