A submerged archeological park still holds the wonders of a Roman Sodom.

A marvel of Byzantine engineering under the streets of Istanbul.

Naturally protected city carved from a rock face.

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.

A beautiful 19th-century Armenian mansion is preserved above an unassuming cafe.

An abused and forgotten metropolis, abandoned for centuries.

This hidden gem is bathed in beautiful natural light.

One of the largest wooden constructions in Europe was meant to be a casino, but soon became an orphanage.

An Art Nouveau gem hides beneath the layers of city grime obscuring this once-magnificent building.

Standing proud atop a Turkish bluff, this Ottoman palace has retained its grandeur despite being abandoned for centuries.

A meow-velous tribute to a beloved street cat, made famous on the internet.

The only residents of this abandoned housing development full of identical castles are stray cats and dogs.

The ornate miniature mansions were built for Istanbul's feathered residents.

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.

This church combines Christian, Byzantine, and ancient Greek architectural elements.

A network of concealed passageways lies within a busy London Underground station.

A relic of Victorian grandeur hides beneath a busy South London road.

The abandoned summer estate of the former Greek Royal Family.

Thousands of rusting train cars have been slowly falling apart on the edge of Greece's second largest city.

An abandoned Byzantine fortress and notorious prison.

An ambiguous ambience emanates from this centuries old leprosy quarantine.

This medieval "painted village" is famous for its geometric facades.