Built as a mausoleum for the Roman Emperor Hadrian in the 2nd century, Castel Sant’Angelo was used as a fortress until it became a papal residence in the 14th century. Located just outside the walls of Vatican City, on the banks of the Tiber River, the towering cylindrical structure is now one of the top tourist attractions in Rome. Castel Sant’Angelo is one of Rome’s most beautiful places to visit after sunset, so consider a Rome night tour to see it fully illuminated. Also, don’t forget to climb up to the rooftop for stunning views of the Eternal City.