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.

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

A psychedelic labyrinth on the San Francisco bay.

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

A huge musical instrument played by the ocean.

Thousands of crosses and markers for soldiers who lost their lives in Iraq and Afghanistan blanket a California hillside.

The former Naval shipyard is open for exploring - mostly.

The perfect spot for a picnic, right next to a giant ballistic missile.

The oldest Naval cemetery on the West Coast.

The timepiece that exonerated a labor radical accused of a parade bombing that killed ten people.

Junkbots and mud babies are the masterpieces in this fantastically sci-fi art museum.