The bunker where Hitler took his own life is hidden under this deliberately ordinary parking lot.

When German-Iraqi relations broke down, this embassy was vacated post haste.

An eerie, derelict amusement park in Berlin.

Cold war icon and onetime "hole" in the iron curtain.

An ancient Viking runestone hidden in plain view in Stockholm's old town.

An ancient passage filled with stalls selling used books, once frequented by Vincent Van Gogh.

One of the largest barracks of the Austro-Hungarian monarchy's military is now an abandoned ruin.

The world's largest historic armory was established by independent citizens to defend themselves from the wars of larger forces.

At high tide this strange footbridge appears to have no purpose whatsoever.

A long spiraling walkway winds through the woods, and around a copper beech tree at the center.

This small exhibition displays equipment and artifacts once belonging to the feared Stasi secret police.

Climb around the high waterfalls on series of iron ladders and bridges within the wildest gorge in the Slovak Paradise.

The Sighignola summit on the Swiss border offers views so breathtaking it's been named one of the most beautiful places in Italy.

Giant WWII fortresses that fired 8,000 rounds a minute, now home to thousands of pigeons.

A small island less than half a mile from Venice is a forbidden island with a dark and twisted past.

Venice's "Island of the Mad."

The ghost town left by the worst nuclear disaster of all time is being taken over by nature and urban explorers.

This derelict superstructure was a very important warning system for the Soviet military.

Vienna's underworld of tunnels and subterranean rivers made an iconic appearance in a 1949 Orson Welles film.

The deepest sinkhole in Central Europe comes with a grisly tale and an unusual nickname: “The Stepmother Abyss.”

This network of conjoined cellars was riddled with traps and supposedly allowed the townspeople to pretend their homes were deserted.

Winding paths and ramshackle mausoleums in the oldest "park cemetery" in London.

Rebuilt remains of a temple to Roman god Mithras.

The final resting place for the remains of 143 Habsburg royalty.