This tiny 19th-century tunnel was built so a man could move his cows from one field to another.

This former luxury resort in Kaua'i is now an abandoned relic.

An abandoned vacation home spent a decade taking on legends. It's now taking on water.

Abandoned silver mine strewn with wrecked and twisted structures.

This massive store is home to an eccentric collection of vintage, retro, and peculiar goods.

The only subterranean ping pong table in Atlanta.

This angular brutalist playground turns playtime into modern art time.

San Francisco's urban bison herd has persisted in the face of extinction, development, and disease.

This concrete tangle of square pipes has stood as a proud thorn in the city's side since the '70s.

A 300-ship graveyard, with a few still visible at low tide.

A tiny theater hidden in an alley plays a constant stream of short silent films for anyone willing to peer through the peephole.

Visible below the waves are memorials to the city's Gold Rush dead.

A pair of slides and a tree-lined stair corridor have been an urban oasis for nearly 40 years.

A shop full of natural curiosities, carnivorous plants, and costumed taxidermied mice.

A collection of 20th-century automata, penny arcade games, and musical contraptions.

San Francisco's newly reopened hands-on science museum.

A museum befitting the city responsible for supplying the majority of the world's LSD.

Its buzzing collection honors vibrator history.

In all of the 29 years it was in operation, no prisoners ever escaped successfully... or so they claim.

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

A psychedelic labyrinth on the San Francisco bay.

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

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

A huge musical instrument played by the ocean.