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

Once the largest windmill outside of Holland, with enormous 114 foot sails.

San Franciscans leave gifts and messages for the magical beings that live behind the tiny, mysterious door installed on a tree in Golden Gate Park.

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

The stones that traveled from Spain to eventually become a holy place for San Francisco's nature worshippers.

An essential stop before plundering, BYO Cutlass.

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

Since 1973, this block has been home to the most concentrated collection of murals in San Francisco.

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

Another of California's unused Cold War missile defense complexes has become a graffiti gallery.

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

Two pillars set 10 paces apart commemorate the "last notable American duel."

A bronze tribute to a legendary Californian, the self-proclaimed "Emperor of the United States."

The peaceful gravesite of a rugged wild west gunman echoes the touching story of his last days.

There's a 12-foot-tall replica of the Washington Monument hidden under a manhole nearby.

Daredevil repair workers can worm their way out the access hatch, loop ropes over the apex and rappel down the monument.

This shrine to bovine consumption and all things fast food is a slice of culinary history both rare and well done.

A perfect circle of twenty-four mysterious holes dates back to prehistoric time.

A community of collapsing homes more than a mile out from the Florida coast.

An abandoned water sports stadium that has become a haven for graffiti and decay.

St Bernard de Clairvaux Episcopal Church, better known as one of the oldest European buildings in the Western Hemisphere.

The only swimming pool listed on the National Register of Historic Places is emptied and refilled each day with naturally filtered water.