Before it was abandoned and left to rust alongside the road, this riverboat starred in a John Wayne movie.

An abandoned car and strange wooden debris are among the scattered remains of the old sand and gravel quarry.

Deco Modern sculptures of the people of the Pacific, cast for the 1939 Golden Gate International Exposition.

Shoot for par over the bodies of the dead on this cemetery-cum-golf course.

Masterful ceramic fountain and map of the Pacific Basin.

Art in the form of a winding, man made crack in stone.

This giant head is all that remains of a once proud statue that survived an earthquake but not a fall off of a wagon.

The taxidermied remains of the "last wild grizzly bear in California" and of the symbol of the state of California.

An enormous illuminated figure dances on the Las Vegas strip.

An elaborate gift from Claus Spreckels is now a piece of San Francisco history.

Radioactivity still cause for concern at this urban explorer's paradise.

This partially buried wreck is one of the most complete of its kind but is only revealed when the sea allows.

Inside an old airplane hangar, friends and strangers alike play on a massive trampoline.

An overlooked and unassuming engineering marvel.

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

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 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.

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

Staircase winds down the side of Telegraph Hill through gardens, wild parrots flying overhead.

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

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

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