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

A nondescript building that's been functioning as a speakeasy for nearly a century and a half.

A collection of 20th-century automata, penny arcade games, and musical contraptions.

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

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

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

Relics of the 1894 Midwinter Exposition continue to delight visitors today.

Its buzzing collection honors vibrator history.

Carnivorous plants, medieval aphrodisiacs, and the largest original wood structure glass conservatory in the western hemisphere.

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

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

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.

Those with a sharp eye can find the hidden image of a German Shepherd on the memorial's Mural Wall.

Legend has it that President Grant’s frequent drinking in the lobby gave rise to the term “lobbyist.”

Members of Congress have traveled between the buildings on Capitol Hill for a century hidden from tourists, press, and storm clouds.

A super-sized promotional trick that is now a D.C. landmark.

The house where John Wilkes Booth conspired with his co-conspirators.

Largest Roman Catholic church in North America.

A Spiritualist house of worship where believers communicate with the dead in the spirit world.

A Civil War fort in the middle of Washington, D.C. has been swallowed by a forest.

The beloved statue at the National Academy of Sciences is oh so inviting to sit on.

This lonely waterfront memorial to the men of the Titanic was erected by the "Women of America."