A hidden subterranean installation offers a view of the sky.

Nestled in the heart of San Francisco’s bustling Financial District stands a unique homage to the Mayan and Beaux Arts.

The remains of a ruined mansion memorialize the 1906 earthquake.

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

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

A modern mechanical planetary system, part of a 10,000 year clock.

The tea room that pushed the boundaries of adorable straight into...we can't find the words.

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

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

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

The seawater playground of gilded-era San Francisco burned to the ground in 1966.

Tiki luxury on Nob Hill.

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

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

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

The only theatre in the world constructed specifically for sound movement.

Get lost in this haunting fairytale art walk through a man-made eucalyptus grove.

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

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.

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

Huge spherical rocks in the middle of the prairie.

A sleepy little town that had the greatest landslide in North American history fall on it.