Trevi Fountain.

This superb late baroque monument represents one of the most famous images of Rome.
Tradition has it that you will return to Rome if you throw a coin into the fountain’s water basin. You should toss it with your right hand over your left shoulder (or left hand over your right shoulder) with your back to the fountain. You’re not allowed to look behind you while you’re tossing the coin but the fountain is so large it’s basically impossible to miss.