This whimsical castle of grottoes was the labor of love of a French postman, and one of the greatest achievements of outsider architecture.

An Italian hillside ghost town.

An artsy hidden staircase leads to breathtaking views of San Francisco.

Bring your own cardboard to the slippery slopes of concrete hidden in a neighborhood park.

An exquisite tunnel of cascading flowers.

An ancient city exhumed from the depths of the ocean.

Every autumn, this hillside is ablaze with red summer cypress.

Malaysian fireflies create a dazzling display as thousands light up in unison.

An isolated dive site teeming with cnidarians.

The ghostly remains of an accidental sea.

The last of its kind in the country.

Ingenious bakery opens up the first Cupcake ATM at their flagship location in Beverly Hills.

Sister store to the Echo Park Time Travel Store.

A Swedenborgian glass church surrounded by redwoods sits perched atop a massive landslide area.

Explore the largest pure gypsum deposit in the world, and go dune sledding while you're at it.

Mother Nature outdoes herself with this stunningly beautiful set of caves carved into marble.

Singing sand that stands as the final remains of an ancient lake.

Abandoned city hidden from the world by tropical forest and isolation on the coast of Kenya.

The stately remains of Llywelyn the Great's mighty fortress.

Machismo turned on its head: the lady's hand goes to the dude with the bigger brain.

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

A 550-square-meter micro-nation off the coast of Britain.

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

A gruesome memorial for those lost in this area during the Khmer Rouge genocide.