A sealed test tube said to hold Thomas Edison's dying breath was given to the inventor's friend and mentee, Henry Ford.

Devastated landscape used for hundreds of years by the Romans as their primary mining site.

A mysterious light floating in the trees of Arkansas may be a piezoelectric effect.

Just below the surface, shrimp are producing temperatures hotter than the sun.

This massive mushroom has spent centuries eating its way across a huge swath of Oregon.

A glowing underwater cliff attracts marine life and divers in equal measure.

The world's brightest bioluminescent bay.

Once the path of a railway tunnel, now home to thousands of glowing insects.

Famous for its bio-luminescent inhabitants, known as "Dismalites" .

Tubing through a cave lit with glowworms is a magical underground experience.

A lake with hundreds of ancient skeletons surrounding it. The surprise is what killed them.

A subterranean ice warehouse that has lain hidden beneath central London for over a century is now open to the public.

The ancient settlement attracts tourists from all over looking to learn about the Chinese vision of the afterlife.

A deadly ancient portal to the underworld.

The world's toughest modern Christian pilgrimage leads directly to the gates of Hell.

Hellam Township is reputed to feature seven remote gates, which when passed through in the right order, open an entrance to hell.

An idyllic hotel that gave its name to a supposed shadow government.

This medieval castle overlooking the Elzbach river looks just like it did hundreds of years ago.

Thousands of tourists and residents in Cologne affix "love padlocks" on the Hohenzollernbrücke Bridge to symbolize their affections.

The Bauhaus-style former industrial complex is considered the world's most beautiful coal mine.

This "floating railway" is one of the world's oldest monorail systems.

Two stunning 17th-century libraries and a cabinet of curiosities.

Underneath this small church are 15,000 bones, arranged by an obsessive academic.

Around 100,000 bodies are buried below the medieval headstones, many of which mark graves with multiple bodies stacked up to 12 deep.