An ornate private entrance to the Vienna subway built specifically for the emperor.

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

Beautiful Austrian natural history museum with carved ceilings and row after row of ancient taxidermy.

Long abandoned underground complex to keep royals safe from a nuclear war that never came.

An ancient Scottish rock formation said to be the gravesite of a giant remains ensconced in legend and intrigue.

Abandoned ship reimagined as a street art canvas.

A hidden tunnel leads to an abandoned slate quarry that's now a secret swimming spot guarded by cliffs.

Following years of secrecy, the hidden history of a World War II site is being brought to light.

The worst flood disaster in Welsh history might have been a lot worse if it had not happened on movie night.

This former military airfield's claim to fame came from a lucky accident during the Second World War.

The remains of centuries of copper mining appear like an alien landscape.

The world's largest prehistoric copper mine had 30,000 animal bones scattered throughout the maze of passageways.

This Welsh village gave itself a ridiculous name in a publicity stunt a century ahead of its time.

The oldest continual pilgrimage site in Britain was supposedly created by a gruesome beheading.

The highest peak in Wales is said to be the final resting place of a giant killed by King Arthur.

The stately remains of Llywelyn the Great's mighty fortress.

A 4,500-year-old forest is slowly being revealed from beneath the sands of a Welsh beach.

Three bridges straddle a stream, one stacked upon the other.

A hermit's tiny cell built into the cliffside that saved him in South Pembrokeshire.

A circle stone within a stone circle.

A gorge full of caverns where early humans lived alongside cave hyenas, giant mammoths and wooly rhinoceroses.

This antique prison is a tourist attraction with a sordid past.

Ancient Egyptian wigs, South American feather headdresses, a bounty of anthropological artifacts in Oxford.

One of the few standing Roman lighthouses and a labyrinth of tunnels are a couple of the secrets at this historic castle.