This East German military command bunker was ready for World War III.

A whimsical and twisted animatronic monster tour beneath the streets of Berlin.

An eerie, derelict amusement park in Berlin.

This jaw-dropping 19th-century bridge uses its reflection to form what appears to be a perfect circle.

The fairy tale castle of the "fairy-tale king."

Hamburgers are intensely proud of their tunnel beneath the river.

Sky ships, planes, and portraits left as unique tokens of hope and thankfulness.

A quarry cum sculpture park where the works of art are chiseled into the very walls.

One of the last realized projects of an influential, self-taught, French Modernist architect Jacques Couëlle.

One of the most powerful religious centers in the Middle Ages, dubbed the founder of Western monasticism.

Sculpture of a legendary French dragon.

A French museum of wrought iron.

The remains of this ornate chapel now act as a portal to a cramped French cemetery.

Experience architect Le Corbusier's modernist design for living in the home he designed for himself.

One of the great treasures of Neolithic art lies within this carefully constructed pile of rocks.

Bordered by forest on three sides and the ocean on the other, the Great Dune of Pilat is the highest sand dune in Europe.

This Corsican Neolithic site is full of pre-Roman megalithic structures that may or may not be penises.

For a brief time in 1960s France, families could climb into a tiny submarine and be pulled along an underwater journey.

Once the hottest nightclub in France, Amnesia now lies in ruins after a 2000 bombing.

This castle-fortress is a living example of the transition from medieval defenses to modern fortifications.

A modern-day Lascaux cave underneath Paris.

The opulent home that inspired Tintin's Marlinspike Hall and the adventures within.

A massive, secret marina for the Nazis' most formidable weapon in the Atlantic.

A Christian retreat founded to welcome refugees fleeing from the Nazis during World War II.