In a 345-million-year-old cave that's 200 feet underground, dinner awaits.

The highest point in Arizona is an oddly snow-topped peak within the otherwise arid state.

A collision of human error and natural geothermal pressure created this rainbow-colored geologic wonder.

An eerie, derelict amusement park in Berlin.

World's first "penitentiary," meant to be humane, drove men insane.

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

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

A kaleidoscopic warehouse-maze of handmade neon signs.

A crumbling hospital from the 1850s on Roosevelt Island.

An exquisite tunnel of cascading flowers.

This astonishingly geometric cave has inspired everyone from Jules Verne to Pink Floyd.

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

La Monte Young and Marian Zazeela's "Dream House" will immerse you in an ever changing world of sound and light.

A terrific purveyor of natural history objects and curios.

A huge musical instrument played by the ocean.

The vast, legendary catacombs hold secrets much stranger than stacked bones.

London's creepiest cemetery was once the site of dueling magicians and mobs of stake-carrying vampire hunters.

A beautiful and abandoned New York subway station from 1904, complete with chandelier.

No one's quite sure why there's a metal megaphone bolted on two rocks in the middle of the Mojave Desert.

The remnants of an early automobile route across shifting sand dunes can still be found in the deserts of Southern California.

Since World War II people have been decorating this stretch of the Yuma desert with signatures arranged out of rocks.

A scrap-metal sculpture recalls an infamous 19th-century camel.

L. Frank Baum wrote part of the "Wizard of Oz" series in this wooden Victorian beach resort.

Erroneously called the world's tallest flagpole, this landmark is devoted to "good neighborliness."