Once the path of a railway tunnel, now home to thousands of glowing insects.

This French "sea of rocks" is packed with stunning rock formations and its own medieval castle.

This jaw-dropping 19th-century bridge uses its reflection to form what appears to be a perfect circle.

A complex of six forts embedded in the Rajasthan hills.

This abandoned fort is said to be the most haunted place in India, so much so that entry is prohibited after sunset.

Five miles of underground river link lake to ocean.

Formerly Yugoslavia's "forbidden island," this sleepy little city still holds the abandoned remains of military strongholds.

A Lycian city of the dead carved into the hillside of Southern Turkey, complete with startlingly human touches.

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

This complex of vertically-excavated Buddhist, Jain, and Hindu monolithic temples in India's Maharashtra providence illustrates a spirit of tolerance characteristic of ancient India.

Rock-hewn monastery complex with hundreds of cave structures tucked away into the mountainside.

Ancient rock-hewn town that witnessed key events of Georgian history.

In paradise, feral pigs have claimed an island all to themselves.

Hundreds of lucky felines haunt the ruins where Caesar was murdered.

The former home of the Nobel Prize-winning American writer is now home to dozens of six-toed cats.

The feral felines of Roosevelt Island have a small army of allies and an abandoned hospital all to themselves.

Exotic feline breeding compound and conservation center.

A tiny microvalley etched into the side of Knocknarea Mountain hides another world.

On Japan's Tashirojima Island, cats are king.

Hidden in plain sight on the Hudson River is an abandoned train station where nature has taken over.

This odd Chilean waterfall-cano hotel must be entered via a rope bridge.

Largest cave system in Africa.

Site full of incredible prehistoric paintings and archeological findings.