The "Four Rivers Fountain" is second only to Rome's Trevi Fountain in its importance and beauty. it's especially spectacular at night. Sitting in the center of Piazza Navona, the fountain dominates the area. At night it is surrounded by visual artists and performance artists as well as guys hawking the latest toy. Grab a table at one of the (pricey) cafes/restaurants that surround the piazza, or take in the atmosphere while you enjoy gelato.