Once the site of the Stadium of Domitian, Ancient Rome's main space for competitive athletics, Piazza Navona is a vast space in the heart of modern Rome best known for its collection of monuments and the buildings that ring its circumference.
Buildings of note include the Sant'Angese in Agone Church, a lovely Baroque church, as well as the elaborate Palazzo Pamphili, built by the powerful Pamphili family and now home to the Brazilian embassy. There is plenty of outdoor seating along the north end of the square, where there are a handful of overpriced restaurants where you are more or less paying for the view.
The fountains are quite possibly the high point of the Piazza Navona. The most central is the Fontana dei Quattro Fiumi, which portrays four river gods poised beneath an Egyptian obelisk. It is meant to represent the spread of Christianity through the four major continents of the time. To the south is the Fontana del Moro, whose main subject is a Moor wrestling a dolphin, while to the north is the Fountain of Neptune, where spear-wielding deity battles an octopus. Yes, the Romans apparently loved to hop in the ocean and take on sea creatures.
Without question a stopping point in every traveler's Rome adventure, Piazza Navona is well worth an hour or two of leisure amongst further examples of art and antiquity; c'mon, this is what this city is all about!