A modern-day Lascaux cave underneath Paris.

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

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

A counter-culture bookstore like no other hides in plain sight in the streets of Paris.

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

The oldest stone house in Paris was built by its most famous alchemist.

Abandoned railway line circling the city of Paris.

In the midst of a living monument to Soviet social engineering, Polish Catholics built this church by hand.

Order “Proletariat’s Cutlet” at this communist-themed restaurant allegedly once visited by Lenin.

One of the world's largest collections of medieval religious art.

A mysterious emblem tucked in an small alleyway is actually the coat of arms of a heroic medieval family.

A World War II torpedo launch station abandoned off the Polish coast.

A floundering Polish shipyard was once the soul of the Solidarity movement that capsized communism.

Boats must transform into railroad cars to navigate this Polish canal.

A haunting deserted hotel is a favorite with artists and photographers.

This hidden collection of everyday objects illustrates life within communist Poland.

A national collection of Communist-era musical posters.

These massive moving sand dunes have swallowed an entire village and are still on the run.

Crosses of all shapes, sizes and colors litter the mountain, the site of a huge yearly Orthodox pilgrimage.

Museum dedicated to "the man who moved the Earth."

A 20th-century picture show in 3-D.

The world’s narrowest house makes for an awkward, four-foot-wide living space.

An abandoned Nazi explosives plant founded by the inventor of dynamite is now an underground museum.

Poland's oldest surviving university building holds a wealth of historic science instruments including some used by Copernicus.