A former military outpost of Ivan the Terrible, the 16th-century church contains some of the rarest examples of Eastern Orthodox mural paintings.

India's first open-air public art district sits in the heart of the country's capital.

The martyr's wax-enhanced skeletal remains lie preserved in a glass case in the Santa Maria della Vittoria in Rome.

Hundreds of notes give thanks to the patron saint of lost causes.

The giant skeleton sculpture is surprisingly well-traveled.

The walls and ceiling of this Polish church are decorated with thousands of skulls, with another 21,000 skeletons just below.

This former quarry is now a picturesque gorge that hides a sunken lake.

The deepest sinkhole in Central Europe comes with a grisly tale and an unusual nickname: “The Stepmother Abyss.”

Europe's largest natural bridge has a 19th century royal chateau built into its side.

A Turkish monastery tucked into a cliff wall.

While not Turkey's deepest underground city, this subterranean redoubt is the largest.

This ancient subterranean megalopolis is known for the hot oil traps that were installed above each of its entrances.

The deepest underground city in Turkey was designed to protect 20,000 people behind massive stone doors.

In this historic region, homes and churches are carved into ancient volcanic rock formations.

An architectural marvel that spans the Arda River, and has stories of a haunted past.

This massive concrete sculpture is said to be the heaviest communist monument on Earth.

The remarkably well-preserved final resting place of a powerful ancient Thracian king.