The Fontana di Trevi; Legend has it that throwing a coin with one's right hand over one's left shoulder ensures that the thrower will return to Rome. Still waiting - but then again, so many other places to visit, never enough time.
Designed in 1732 by Nicola Salvi, it depicts Neptune on a giant clam shell led by Triton and sea horses. The fountain's water comes from a 1st-century-BC underground aqueduct, and the name Trevi refers to the tre vie (three roads) that converge at the fountain.