This tunnel entrance is built to resemble a grand castle but no one is quite sure why.

If you want to talk to the Pope you will have to stare down this surreal vision of Jesus rising from a nuclear hell.

The end of the 4 Line is also the end of the line for 300,000 souls in one of NYC's most illustrious cemeteries.

The once forbidden "secret cabinet" of erotic art from excavations of Pompeii and Herculaneum.

A unique collection of Soviet military artifacts lies hidden away in a disused train, in the unrecognized Eastern European republic of Transnistria.

The largest medical and anatomical collection in France lies hidden from the public.

A treasure trove of pathological, forensic, parasitological, and anatomical specimens.

A unique hanging cable-car navigates through Dresden, the oldest suspension railway in the world.

This Dresden church was purposely rebuilt Protestant after being demolished in World War II.

The remains of a failed attempt at medieval nerdery are hidden deep in the woods of Virginia.

Once described as the "Eagle's Nest," this ruined ancient city rests on a remote mountaintop.

Running under an entire mountain, the longest highway tunnel in North America is kept fresh using portal fans and jet fans.

This small city where almost everyone lives in the same building can only be reached via North America's longest tunnel.

This Italian foot path winds through the mountains via 52 individual tunnels.

This Nazi-built amphitheater was constructed on a sacred mountain site used by various German cults.

The highest point in Washington state is a volcano covered in glaciers.

When Croatia became independent of Yugoslavia, the splintering governments left behind these concrete tunnels.

Formerly Yugoslavia's "forbidden island," this sleepy little city still holds the abandoned remains of military strongholds.

The highest peak in Utah is the hardest to reach, but only if explorers choose the hard way.

These powerful, if squat, Canadian waterfalls flow in different directions depending on the time of day.

This series of underground chambers contains Europe's largest subterranean lake that is slowly drained each day.

These bronze pamphlets remember a remarkable group of Germans who fearlessly opposed the Nazis in the very center of their power.

This wooden hotel is a temple to German sustainability and forest conservation.

This collection of over 50 murals celebrates Brussels' rich history as the self-proclaimed home of the "comic strip."