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

Mysterious and ancient carved standing stones.

A brightly colored natural bridge formed by mineral-rich hot springs high up in the Andes.

A neo-Gothic castle in the Argentinian countryside.

A toxic lake near a volcanic caldera that is home to flamingos and other life.

This natural history collection contains the bones of a circus elephant that seem to be chasing a whale skeleton.

Guitar made of trees, dedicated to a man's lost love.

This magnificent abandoned hotel has long been haunted by its Nazi past.

One man's quest to collect artifacts from every aspect of human life has resulted in this eclectic Argentinian museum.

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

London's creepiest cemetery was once the site of dueling magicians and mobs of stake-carrying vampire hunters.

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

The mysterious, fantastical woodland inspiration for "The Lord of the Rings."

"Only the devil could play golf here."

Huge spherical rocks in the middle of the prairie.

This beautifully verdant lagoon is tucked below a massive volcano in a crater atop a black pebble beach.

Crushed coral and crystals give the sand its signature coloration.

One of the most extreme deserts in the world, these snow-free valleys harbor life, despite the hostile environment.

Scientists use one of the saltiest bodies of water on Earth as a terrestrial base for studying water on Mars.

The inky volcanic sand leads to reefs teeming with aquatic life waiting to be discovered by snorkelers and divers.

Whimsical sculptures and caves chiseled by nature over the millennia.

In Northeastern Iceland lies something of an oxymoron: a steaming desert.

This army of concretions is an unexplained geological phenomenon unlike anything else in the world.

Crooked windswept pines give this old forest an enchanted and magical look.