You cannot miss this fountain, as it's by the Duomo and the Bell tower on the main Duomo Sq.
It was built in 16 cent to celebrate the opening of the city's aqueduct. It's another example of marvelous highly detailed fountains. Unfortunately, an iron fence around it spoils the view.
The Fountain is part of the expansive plaza that surrounds the Cathedral and the magnificent mechanical clock tower. Crowds gather at noon each day to watch the figures of the clock move. It's a delightful spot to visit for twenty minutes or so.