A Turkish monastery tucked into a cliff wall.

Naturally protected city carved from a rock face.

Ottoman-era houses lovingly preserved.

Once described as the "Eagle's Nest," this ruined ancient city rests on a remote mountaintop.

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

Live a night as a Byzantine King, with a minibar and private jacuzzi.

Hidden just under the waters around this Turkish island are the ruins of a once great city.

A Turkish ghost town abandoned in a population exchange with Greece.

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

An abused and forgotten metropolis, abandoned for centuries.

This famous city eluded concrete detection until the early 2000's.

A deadly ancient portal to the underworld.

This hunter-gatherer architecture is believed to be the oldest religious complex known.

These tombs were built into the side of a mountain so that ancient angels could reach the dead.

A marvel of Byzantine engineering under the streets of Istanbul.

Roman ruins top white travertine terraces formed by ancient hot springs.

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

The underground sanctuary of a mysterious ancient cult.

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

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

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."

Two very green residential towers cleaning the air in one of Europe's most polluted cities.