This 1,300 year old monastery built atop a single rock was once only accessible depending on the whims of the tide.

For two weeks every June, fireflies in the Smoky Mountains perform an astonishing light show.

A roaring, awe-inspiring double cascade of icy water flows through woodland Oregon like something out of a Tolkien novel.

Amid the bustle and noise of the Financial District hides a secluded garden oasis above the city streets.

A church of bones, decorated with 40,000 human skeletons.

These fantastically named natural pools look like something out of a Scottish myth.

An enormous, inside-out glass globe built in 1935.

Hot springs monkey spa in the middle of Hell's Valley.

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

A 140-year-old castle with underground caves hidden in San Francisco.

The fairy tale castle of the "fairy-tale king."

The intricate stonework of Machu Picchu serves as a testament to Incan engineers.

The sound of swaying stalks in this stunning grove has been named a governmentally recognized sound.

An Italian crevasse filled with abandoned buildings gives visitors a look at the world without humans.

An emerald-green grotto just a short trip from Austin.

This jaw-dropping 19th-century bridge uses its reflection to form what appears to be a perfect circle.

Most-visited and most-photographed slot canyon in the American Southwest.

On the Oregon coast there is a natural hole that seems to be draining the sea.

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

A huge musical instrument played by the ocean.

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