With its chunky round keep, this castle is an instantly recognisable landmark. Built as a mausoleum for the emperor Hadrian, it was converted into a papal fortress in the 6th century and named after an angelic vision that Pope Gregory the Great had in 590. Nowadays, it houses the Museo Nazionale di Castel Sant'Angelo and its eclectic collection of paintings, sculpture, military memorabilia and medieval firearms.
Many of these weapons were used by soldiers fighting to protect the castle, which, thanks to a secret 13th-century passageway to the Vatican (the Passetto di Borgo), provided sanctuary to many popes in times of danger. Most famously, Pope Clemente VI holed up here during the 1527 sack of Rome.
The castle's upper floors are filled with elegant Renaissance interiors, including the lavish Sala Paolina with frescoes depicting episodes from the life of Alexander the Great. Two storeys up, the terrace, immortalised by Puccini in his opera Tosca, offers unforgettable views over Rome.
Note that ticket prices may increase during temporary exhibitions.