The Vatican Museums are one of the world's greatest collections — dozens of galleries of classical sculpture, tapestries, maps, and Renaissance painting leading to the Sistine Chapel. The Laocoön group, the Apollo Belvedere, and Raphael's Stanze are highlights before you even reach the chapel. The Sistine ceiling (Michelangelo, 1508–12) is everything it's supposed to be; the Last Judgement on the altar wall is even more arresting.
Book online — the queue without a ticket can stretch hours. An early morning slot gets you into the Sistine Chapel before tour groups turn it into a rugby scrum. Budget at least three to four hours for the full circuit.