The popes' art collections, ending in the Sistine Chapel, where Michelangelo painted the ceiling and the Last Judgement.
From Monti take metro B to Termini, change to line A and ride to Ottaviano, then walk 10 minutes; allow 40 minutes door to door, or a taxi of about €15–20.
Open Monday to Saturday 08:00–19:00, last entry 17:00, closed on Sundays; the ticket is €20 plus €5 for booking online. Allow three hours: the route to the Sistine Chapel is one way and long, and the Raphael Rooms come just before it.
In the chapel itself there are no photos and guards ask for silence. The 08:00 slot is the quietest hour in the Sistine Chapel on a Saturday, if you are willing to start an hour earlier.