Bottom line: choose the Vatican Museums if you love Renaissance art and papal treasures; choose the Colosseum if you're drawn to ancient Roman history. The Vatican Museums are a treasure trove of Michelangelo and Raphael — highlights include the Sistine Chapel's Creation of Adam and Last Judgment, Raphael's School of Athens, and the 120-metre Gallery of Maps — but they draw huge crowds, photography is banned inside the chapel, and you must book a timed-entry ticket in advance. The Colosseum, built in the 1st century AD, was the stage for gladiators and Roman power; an arena-floor ticket lets you walk the gladiators' path and peer into the underground hypogeum. Go early morning or at golden hour to beat the crowds. If you're very short on time: pick the Vatican for art (quieter in the late afternoon) or the Colosseum for ancient atmosphere. Book both online ahead.