Tucked into the slope below the Duomo's apse, reached by a staircase down from the cathedral, the Baptistery is a single high vaulted room with one of the great Renaissance objects in Italy: a marble and gilt-bronze hexagonal font (1417–1431). Its panels are shared between three of the era's giants — Lorenzo Ghiberti, Donatello, and Jacopo della Quercia — and the small carvings on the corner pilasters and frieze are full of surprises.
Frescoes by Lorenzo di Pietro (Vecchietta) cover the vault. A combined ticket with the Duomo is the easiest way in.