A fortified medieval basilica on the Caelian Hill preserves extraordinary frescoes and one of Rome's most beautiful hidden cloisters.

The only remaining arch of the oldest stone bridge in Rome stands in the middle of the Tiber.

A burial vault located under Tiber Island in the middle of the Italian capital.

This small, ancient Roman temple was once a church dedicated to the patron saint of penitents.

Its interior is adorned with some of the best examples of early Christian mosaics.

Stone memorial that's said to predict the death of the pope and the site of the Cadaver Synod.

This hydrochronometer was invented by a Dominican monk and is a prime feature in this garden.

Remnants of a 4th-century church with vivid medieval frescoes and ancient sarcophagi hide beneath this old basilica.

This gallery commissioned by Cardinal Spada is known for its magnificent optical illusion.

Also known as the Square Colosseum, this building is a prime example of fascist-era rationalist architecture.

This is the oldest Roman-made bridge in the city still existing in its original state.

This park on the outskirts of Rome boasts two ancient Roman aqueducts and a medieval tower.

The ruins of an abbey believed to have been founded by Charlemagne in the 9th century.

This ancient market is often referred to as the oldest shopping mall in the world.

Gods clash with machines in a power plant regenerated as a museum.

The best preserved Paleochristian basilica in Rome hides a number of oddities and secrets.

A magnificent waterfall is also home to the remains of a Roman hydraulic engineering system.

An immersive projection art installation uses sound, scale, and light to take visitors inside classic works of art.

The narrowest street in Paris.

The oldest continual pilgrimage site in Britain was supposedly created by a gruesome beheading.

The highest peak in Wales is said to be the final resting place of a giant killed by King Arthur.

Derelict chemical plant on the North Sea is a beautiful industrial ruin.

Built during the Scottish boom in the oil industry, the village was never inhabited.

This hidden rooftop garden in downtown London offers a quiet respite from a bustling city.