The Trevi square (piazza) and fountain are model examples of public space and art. The square is constantly filled with tourists (and hawkers) so there is a consistent buzz and high level of energy. The fountain is not your typical round thing with water squirting up, it is a massive, multidimensional and functional work of art. Be sure to throw a coin over your shoulder back into the fountain to ensure that you return someday (old travelers tale). Also, watch out for pickpockets in the square, that tip is from an experienced modern day traveler.