A museum dedicated to a secret military hospital hidden beneath a castle in Budapest.

A Parisian cemetery where the elite and artistic are interred beneath an eccentric collection of tombs.

Notorious artist squat renovated into legal studios.

The celebrated eyesore created by starry-eyed sweethearts.

The very center of Paris is surrounded by a bevy of strange good luck rituals.

Budapest's Communist-era statues, banished to the suburbs.

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

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

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

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

One of the most spectacular canyons in the world.

Traditional 11th-century outdoor tannery.

The ancient latrines of the Greeks, in all their public glory.

Once an opulent Art Nouveau hotspot, the Constanța Casino is one of Romania's most beautiful abandoned buildings.

Giant marble phalluses on the sacred island of antiquity.

This ancient Greek place of assembly and marketplace is being revealed layer by layer below the modern Athens cityscape.

An awe-inspiring mosque in Morocco with one of the tallest minarets in the world.

An Albanian monument to the Communism that nearly crushed the country is now a crumbling wreck.

What happens when you cross a mayor and a painter?

Hundreds of thousands of concrete bunkers crowd Albania long after the fall of Communism.

Single runway interrupted by a busy road that cuts across its middle.

Three bridges and one giant canyon make up this fantastic Spanish settlement.

The final resting place of the great navigator, or maybe his brother.

This iconic Parisian bookstore doubles as the "Tumbleweed Hotel" for traveling writers.