The quirky gift from West Berlin for the 1968 World's Fair still stands in Hemisfair Park.

This museum showcases the history and contributions of the U.S. Army to the medical industry, both on the battlefield and off.

Clean, cold drinking water flows from a nondescript pipe in a roadside rock face.

Often mistaken for an office building, inside this venue is an amazing collection of Native Alaskan art.

The king of U.S. high points towers over every other peak on the continent.

Upside-down trees serve as natural flower pots in this hanging garden of Alaska.

This frozen tunnel in central Alaska is both an engineering feat and a valuable climate classroom.

A tiny museum housed in a New York freight elevator specializes in the "overlooked, dismissed, or ignored."

At a museum of everyday objects, it is the act of collecting that is really on display.

A colorful "forest" made entirely from three tons of recycled plastic waste.

With the touch of a button, you can read a randomly selected short story.

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

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

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

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.

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

A psychedelic labyrinth on the San Francisco bay.

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

Secret US military film studio in the Hollywood Hills.

A treasure hunter's tiny bar, harboring celebrities since 1959.

A museum dedicated to exhibiting remarkable outsider art.

World's largest collection of serial killer artwork and other macabre exhibits.

Non-profit time travel mart sells goods you would need for a trip through the fourth dimension.