Castel Sant'Angelo (Museo Nazionale)

Hadrian's mausoleum (139 AD) turned papal fortress, prison, and museum. The interior takes you through ancient Roman corridors, Renaissance papal apartments with frescoes by Pinturicchio, the prison cells where Cellini and Cagliostro were held, and the rooftop with its bronze archangel statue. Connected to the Vatican by the Passetto, the elevated escape corridor used by Pope Clement VII to flee the 1527 Sack of Rome. Closed Mondays.