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

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

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

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

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

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.

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

A psychedelic labyrinth on the San Francisco bay.

A huge musical instrument played by the ocean.

A collection of more than 12,000 shoes, displayed in a building shaped like a shoebox.

This Parisian fountain is a little bit fantasy and a little bit nightclub.

The world's only museum devoted solely to the art and collection of action figures.

A whimsical and twisted animatronic monster tour beneath the streets of Berlin.

Art and a pun, all in one.

This unique exhibit "Dialogue in the Dark" reverses roles as the visionless become guides and the sighted become ‘blind.’

After years of being casually peed on by humans, this tree is peeing back.

This walkway is so narrow it needs its own light to stop pedestrian traffic jams.

A bus with a butt and biceps to put Olympic athletes to shame.

What looks like a crashed Zeppelin is actually a bright, airy reading room perched atop a modern museum.

An Orwellian sculpture with eyeball cameras watches passersby.

This doorless 20th-century elevator doesn't stop or slow down.

Street artists transformed an abandoned air vent into the beloved Star Wars robot.

Despite attempts by local police to discourage it, Beatles-inspired graffiti has been a means for artists to air grievances for decades.