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

A kaleidoscopic warehouse-maze of handmade neon signs.

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

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

The neon signs from Las Vegas' past find their final resting place at this unusual graveyard.

A collision of human error and natural geothermal pressure created this rainbow-colored geologic wonder.

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

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

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

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

An exquisite tunnel of cascading flowers.

On Japan's Tashirojima Island, cats are king.

Rippling sand dunes frozen in the Arizona rock.

Non-profit time travel mart sells goods you would need for a trip through the fourth dimension.

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

A psychedelic labyrinth on the San Francisco bay.

A suspended footbridge allows for traversing this gorge carved through the French Alps.

This crack in France's seaside cliffs once hid a sinister secret.

Take black faced bears with giant clubs, white faced barbers wielding axes, hunters armed with shotguns, and mix in a lot of drinking.

Trek up this glacier before it disappears.

The birthplace of the ferocious William the Conqueror, this castle is awash in medieval history.

Tens of thousands of ancient rock carvings hidden in the heart of a French national park.

An often-shuddersome journey into a low-tech, robotic themepark.

Bordered by forest on three sides and the ocean on the other, the Great Dune of Pilat is the highest sand dune in Europe.