Cappadocia, Turkey

Located in central Turkey, the Cappadocia region is home to 36 underground cities! At a depth of approximately 85 m (280 ft), Derinkuyu is the deepest.

Made up of seven underground levels, this city once housed up to 20,000 people.

The city had everything for a civilization, including shops, living quarters, schools, ventilation shafts, wells, kitchens, oil presses, a bathhouse, storage rooms, and even primitive wineries.

In case of any threat, each level of the city could be sealed off using monolithic stone doors.

The city was discovered in 1963, when a local man reportedly stumbled upon some tunnels while renovating his home. It opened to the public two years later, though less than half is actually accessible.

Matmata, Tunisia

Over 2,000 inhabitants live there full-time.

The buildings were created by digging a big pit and carving out artificial cave walls to make a living space.

Though the underground complex was only rediscovered in 1967, it had already become quite famous.

The underground city was also featured in 'Attack of the Clones.'

Petra, Jordan

The ancient Nabataeans hand-chiseled the sandstone hillsides into an impressive collection of rooms, tombs, halls, and temples.

Petra is also known for its cameo in the film 'Indiana Jones and the Last Crusade.'

Excavators believe that the vast majority of Petra's ruins may still lurk underground.

Coober Pedy, Australia

The dugouts and mines exist alongside homes, shops, restaurants, hotels, museums, churches, a casino, a gift shop, and even a local pub.

The town, which has one of the few underground churches in the world, produces more than 80% of the world’s opals.

Matera, Italy

Sassi di Matera, which means "stones of Matera," is the area of prehistoric cave dwellings in the southern Italian city of Matera.

The houses, as this historical replica shows, are dug into the calcareous rock itself.

Soon, the low levels of light and high concentration of disease began to create slum-like conditions, and the residents struggled in poverty.

Between 1953 and 1968, the cave-dwellers were moved into modern housing, but a more recent spike in tourism, and the flourishing of Matera's artistic community, have led to a reclamation of the land.

Naours, France

Two miles of tunnels and more than 300 man-made rooms rest some 30 m (100 ft) beneath a forested plateau in northern France.

The site was built around the third century CE as part of a Roman quarry, but it was later expanded into a subterranean village after locals began using it as a hiding place during the wars of the Middle Ages.