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 5th 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 Battisteroin 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 have been undergoing restoration since 2014, and upon completion will be moved to inside the Opera del Duomo museum. Replicas are currently in their place.

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 6:30 p.m.; on Saturday from 8:15 a.m. to 6:30 p.m. and Sunday from 8:15 a.m. to 1:30 p.m. The OPA 24-hour pass is 15 euros (or about $18), and also grants you admission to the Duomo and the cupola climb. For more information, visit the Baptistery section of the Florence tourism website.