Ancient ruins hidden underneath a modern luxury hotel.

The first Russian Orthodox church in the Catholic city of Rome in almost a thousand years.

A treasure trove of Renaissance-era funerary art in a Roman church built on top of Nero's grave.

A Nesting Doll of Churches.

This ritzy Italian market is built around a statue of an unforgiven heretic who was burned for his belief in an endless universe.

Jesus' footprints and the first catacombs in the world.

2300-year-old Roman road connecting the empire.

This hidden Art Nouveau courtyard is an opulent feast for the eyes.

A master of trompe-l'oeil creates a stunning, tourist-fooling dome out of a flat ceiling.

Architectureal fantasy quarter of Rome.

An alchemist's “magic door” stands in the middle of a Roman park.

The crypts of Capuchin friars decorated with the bones of over 4,000 friars, including an entire "crypt of pelvises."

The capital of Cambodia is named after the hill on which this ancient temple complex stands.

Khmer Rouge's high security prison.

5,000 skulls in memorial to those killed by the Khmer Rouge.

This collection of reclaimed landmines acts as both an exhibition of their deadly history and as a shelter for children affected by them.

A small 12th-century temple surrounded by waters believed to have curative properties.

A battle between nature and architecture in the Cambodian jungle.

A secluded art gallery hidden within the cellars beneath Tallinn’s medieval monastery.

The Guardian of Tallinn.

The oldest church in the Estonian capital is home to over 100 fantastical cemetery coats-of-arms.

Only a fragment of this 15th-century Dance of Death survives today.

A forest park outside Tallinn full of architectural and artistic curiosities.

This medieval Estonian tower provides access to a series of tunnels that have been home to soldiers, punks, and fine art.