Below a historic English market town lies a secret underground city complete with kitchens, laundries, storerooms, and an underground lake.

There's a labyrinth of manmade tunnels stretching for over an acre beneath Bristol.

The abandoned funicular tunnel was a secret base for the BBC during World War II.

One of the largest megalithic complexes in England, which local legend holds is a wedding party turned to stone by the Devil.

Cathedral-like Victorian vaults are hidden within this iconic bridge.

A nuclear bunker built to shelter the politicians and important people of Scotland in case of nuclear attack.

On a site with a long military history, a 1980s shelter.

The castle was reconstructed to fit Kaiser Wilhelm II's romanticized vision of the Middle Ages.

One of the world's most complex timepieces.