Castel Sant'Angelo

Few buildings in Rome have lived as many lives as Castel Sant'Angelo. It began in the second century as the mausoleum of the emperor Hadrian, a colossal drum of stone on the right bank of the Tiber, finished after his death and used as the tomb of emperors for decades afterwards. When the empire faded, its massive walls made it the obvious stronghold of the city, and for more than a thousand years it served as a fortress, a prison, a treasury and a refuge for the popes, who could reach it from the Vatican along the Passetto di Borgo, a fortified elevated corridor running along the old city wall. In 1527, during the Sack of Rome, Pope Clement VII fled along that corridor and held out inside while the city was looted. The name comes from a legend: in 590, as plague ravaged Rome, Pope Gregory the Great is said to have seen the Archangel Michael on the summit sheathing his sword, a sign that the epidemic was over. A bronze angel has crowned the building ever since, the current one dating from the eighteenth century. Today it is a national museum, and a visit is a walk upward through time. You enter at the level of the Roman tomb, climb the ancient spiral ramp that once led to the burial chamber, then rise through medieval ramparts, papal prisons and storerooms to the Renaissance apartments, where frescoed halls such as the Sala Paolina show how luxuriously the popes lived when they were not under siege. At the top, the Terrace of the Angel opens onto a panorama that takes in the dome of St Peter's, the river and the rooftops of the centro storico. Opera lovers know it as the setting for the final act of Puccini's Tosca, whose heroine leaps from these battlements.

The approach is part of the experience. Cross the pedestrian Ponte Sant'Angelo, the ancient Aelian bridge lined with ten Baroque angels carrying the instruments of the Passion, designed by Bernini and carved by his workshop, and the castle rises directly ahead. Inside, the route is mostly one way and largely uphill, on ramps and stairs, so allow time and wear comfortable shoes. The lower levels are atmospheric but sparse; the interest builds as you climb. Look out for the Cortile dell'Angelo, the courtyard where the earlier marble angel now stands, the cannonballs stacked in the courtyards, and the papal bathroom of Clement VII, a small room with delicate painted decoration. The Passetto di Borgo is normally closed and opens only for occasional special visits, so do not count on walking it.

Tickets: the Tiqets venue page sells entry tickets and tours, and booking ahead is sensible in high season, when the security line on the riverside can be long. According to the ticketing information, the castle is closed on Mondays and on 1 January, 1 May and 25 December, entry is free for visitors under 18, and admission is free for everyone on the first Sunday of the month, when queues are at their worst. Hours and rules change, so check before you go. There is a bar with a terrace partway up, which is a pleasant place for a coffee with a view.

Castel Sant'Angelo works brilliantly as a bridge between days. It sits a ten-minute walk from St Peter's Square along Via della Conciliazione, and just across the river from Piazza Navona and the centro storico, so many visitors fit it in after the Vatican, when the light softens and the terrace is at its best. Families find it one of the most engaging monuments in Rome: it is a real castle, with ramparts, cannons and prisons, and children enjoy the climb. History buffs get Hadrian, the medieval papacy and the Renaissance under one roof. For couples, the walk back across the angel bridge at dusk, with the dome of St Peter's behind you, is one of the loveliest moments in the city.