Deep in the limestone cliffs of the Alabaster Coast, a German fortress built during World War II.

These rustic holiday homes are made from discarded fishing boat hulls.

This miniature take on the Kremlin is one Dutch man's retirement project.

This recently restored crypt was once plagued by liquefying coffins and exploding caskets.

This historical Netherlands fortress still bears the marks of its single siege.

Incredible labyrinth of man made caves.

A unique zoological park home to over 30 species of wild cats, both big and small.

Abandoned since 1998, this train station has become an oasis for urban explorers.

This disused boat elevator was saved from the scrap heap so that visitors could tour its rusting skeleton.

An underground city of ancient quarry tunnels hid thousands of Allied soldiers in WWI.

A Cold War command center is hidden under an idyllic countryside.

The sculpture is made of more than 100,000 knives collected to raise awareness about violence.

A metal tree emits eerie, melodic notes on top of Lancashire's Crown Point.

The largest greenhouse in the world is home to over one million types of plants.

Surreal riveted sea forts once protected the Kent shores from German attack.

The hidden "ballroom" under a mansion lake was built by a criminal who ate a cyanide pill during his trial.

Hidden beneath the streets of London is a secret subway that only carried mail.

The sign at the garden gate reads: "These Plants Can Kill."

One of the few remaining casualties of the London Blitz, this destroyed church has become an enchanting public garden.

This ornate Victorian marketplace was the setting for Diagon Alley and the Leaky Cauldron in the Harry Potter films.

This astonishingly geometric cave has inspired everyone from Jules Verne to Pink Floyd.

The world's tallest boat lift stands as a massive piece of industrial tourism.

A rare example of World War I trenches from the British front.

The site where one of the most famous poems of World War I was composed is preserved to honor the legacy of the work.