A scandalous Art Nouveau collaboration that set Paris all atwitter at the turn of the century.

The ruins of a Duke's bucolic dream, where camels once roamed alongside "Dutch" windmills and faux-Italian vineyards.

The vast, legendary catacombs hold secrets much stranger than stacked bones.

Paris' linguistic guide to the international language of, yes, love.

This Parisian fountain is a little bit fantasy and a little bit nightclub.

Indents in the pavement are all that remain from a grisly death machine in Paris.

Remains of Roman amphitheater hidden in a sleepy quarter of Paris.

This massive library holds what was once the largest book collection in the world.

Noirish green neon marks the location of one of the oldest private detective agencies in France.

A lone cannonball remains lodged in the walls of the Hotel de Sens as a sober reminder of a revolution.

Notorious artist squat renovated into legal studios.

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

Abandoned waterpark turned counter-culture mecca.

This imposing modern citadel started out as a home renovation project.

Cursed swimming pool left abandoned is now a favorite of filmmakers and ghost hunters.

Mountain where Jesus was first tempted by the Devil.

This semi-secret storybook hedge maze is also the oldest garden in the city.

A vista of the city and sea from atop the little-known viewing deck on an unassuming Columbus statue.

These secluded and abandoned anti-aircraft defenses have become one the most scenic viewpoints in Barcelona.

A beautiful but toxic fountain of mercury.

The neon signs from Las Vegas' past find their final resting place at this unusual graveyard.

One of the deepest indoor swimming pools in the world.

The convergence of two currents makes this a surprisingly pleasant getaway in the Arctic Circle.

This Industrial Age architectural and engineering gem helps visitors and residents alike traverse Lisbon, “The City of Seven Hills.”