The Battistero is the oldest building in the city, and although the current façade dates from the 11th century, historians have dated the Baptistery back to the fifth century. It hasn't been proven, but many say that this octagonal building was once a temple dedicated to Mars, the Roman god of war.

Today, this ancient building is a must-do for any art lover. Wake up early to beat the crowds, who flock to the Battistero in search of the Gates of Paradise. Designer Lorenzo Ghiberti's delicate depictions of Christ and other religious symbols on these massive doors inspired awe in even the most renowned artists, including Michelangelo, whose praise of the doors earned them their name. Note: the doors at the Baptistery are replicas of the originals. If you would like to see the originals, you'll have to pay a visit to the Museo dell'Opera del Duomo, which can be found just a short walk behind the Baptistery.

Once you get inside the Baptistery, recent visitors advised that you spend plenty of time looking up: The ceiling is covered with intricate frescoes.

The Baptistery sits near the Duomo in the Piazza San Giovanni. It is open to visitors Monday through Friday from 8:15 to 10:15 a.m. and from 11:15 a.m. to 7:30 p.m.; on Saturday from 8:15 a.m. to 7:30 p.m. and Sunday from 8:15 a.m. to 1:30 p.m. Note that it is closed on the first Tuesday of every month. Tickets, which cost 18 euros (about $20), grant you admission to all five monuments in Piazza Duomo, including the cupola climb. They must be reserved in advance online. For more information, visit the Baptistery section of the Duomo website.