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.

Not merely a museum – but a whirring powerhouse that offers a subterranean peek into the heart and soul of cable car operations.

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

A monument to the love people have for their pets.

An overlooked and unassuming engineering marvel.

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

Big gun installations, built over a massive cemetery, now abandoned & hidden in trees.

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

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.

Olfactory delights in San Francisco's Botanical Gardens.

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

Its buzzing collection honors vibrator history.

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

A psychedelic labyrinth on the San Francisco bay.

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.

Historic psychiatric asylum and most-filmed location in the Great White North.

This former iron ore mine comes alive with fascinating stories of its history.

A long-abandoned provincial prison left to crumble in the frigid air of Ontario.

A small and quirky museum hidden inside a fence.

Despite being dead since the 1970s, this Canadian tree is kept upright and intact by adoring locals.

This hauntingly stark structure is a relic of an industrial past.