Part of every Roman visit!
All of Vatican City is a treat to see, there are two visits that many miss however, the first is the dome of Saint Peter's you must climb about three hundred stairs sort of sideways at times but it is so totally worth it. The sights inside and out are worth every second of the climb.
The second stop which most who are not local know not about is a small outdoor/indoor cafe called Vitorio's, ask Vatican workers for directions. It is just outside the great arm's of St Peter's square as you head toward the North American College