Assemble a masterpiece at the first and only North American school exclusively dedicated to mosaic art.

Gold Rush-era tombstones line the park's paths.

The randomness of this wall of lava lamps helps encrypt up to 10 percent of the internet.

This shop and studio is dedicated to the art of the book, from letterpress to bookbinding.

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

The oldest burial ground in the city, final resting place of city founders, Ohlone natives and murderers alike.

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

The last remaining relic of San Francisco's glittering 1915 Panama Pacific Exposition.

Big gun installations, built over a massive cemetery, now abandoned & hidden in trees.

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

The one-time watch house for incoming ships at the Golden Gate now stands abandoned and hidden in trees.

A favorite haunt of dinosaur loving children and hallucinogen loving hippies alike.

A walk-in working camera obscura produces 360-degree live images of the San Francisco coast.

Its buzzing collection honors vibrator history.

This shop specializes in oddities and Victorian-inspired wonders.

A winding path built in secret on the edge of the continent.

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

A huge musical instrument played by the ocean.

The boulder on which Alexander Hamilton laid his head as he died can still be visited on the New Jersey coast.

The remains of a 19th century spring, and the site of an infamous unsolved murder.

A crumbling hospital from the 1850s on Roosevelt Island.

The remnants of two World's Fairs are here, complete with a 12-story globe, a mini-Manhattan, and a UFO-shaped pavilion.

Hidden in plain sight on the Hudson River is an abandoned train station where nature has taken over.

When ecosystems collide in the arid Southwest.