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.

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

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

A psychedelic labyrinth on the San Francisco bay.

A huge musical instrument played by the ocean.

A Cold War site complete with rusty structures, hiking trails, and beautiful views.

This symbol of peace is appropriately positioned overlooking the Pacific Ocean.

A hospital closed seemingly in the middle of operations, leaving behind fodder for horror films and ghost hunters.

Semi-recognized center of the world, with many oddities.

Once the site of the Hawaiian monarchy, this building was originally designed as a palace.

This narrow coastline trail through the dense Kauai wilderness is among the most beautiful and dangerous in the world.

Earth's tallest volcano is sacred to Native Hawaiians, and home to a dozen world-class observatories.

The randomness of this wall of lava lamps helps encrypt up to 10 percent of the internet.

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

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

This sun-scorched lakebed contains samples of half the natural elements known to humankind.

A volcanic tunnel illuminated by natural skylights offers a shaded respite from the desert sun.

The largest dune field in the Mojave offers a chance of hearing the 'singing sands.'

A 250 million-year-old rock formation has earned a rather unique nickname.

You don't have to be a diplomat to visit the so-called Camp David of the West.

Hike amid the palm trees that thrive among Southern California's Indio Hills.

This former stomping grounds of the most eminent astronomers of the early 20th century.

Named after a bandit and the star of several Hollywood prehistoric landscapes, these sandstone formations are a historical part of the Los Angeles natural landscape.