This medieval castle overlooking the Elzbach river looks just like it did hundreds of years ago.

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

This beautiful building in the heart of Manhattan's Financial District was empty for decades.

An enormous, inside-out glass globe built in 1935.

The sound of swaying stalks in this stunning grove has been named a governmentally recognized sound.

A miniature rainforest is growing inside of a Midtown Manhattan office building.

Amid the bustle and noise of the Financial District hides a secluded garden oasis above the city streets.

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

The installation’s official name, “You Who Are Getting Obliterated in the Dancing Swarm of Fireflies,” says it all.

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

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

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

A huge musical instrument played by the ocean.

A kaleidoscopic warehouse-maze of handmade neon signs.

A beautiful Victorian statue shows France's enduring love of the rhinoceros.

Collection of antique taxidermy and natural specimens, near one of Paris's oldest flea markets.

Former hunting lodge of a duke who was an avid collector of impressionist works.

A French artist's vague warning hangs over Belleville.

In this Parisian garden's grotesque former life as a zoo it fed exotic animals to the bourgeois and put humans on exhibit.

Architect Le Corbusier built his friend a cubist house to match his impressive collection of cubist art.

Two awe-inspiring globes from the reign of the Sun King hang from the ceiling of France's national library.

Twelve grave-faced marble angels guard the emperor's tomb at Les Invalides.

Hidden away in a modern library are the remains of one of the 18th century's most celebrated wunderkammers.

A Parisian exterminator's shop whose storefront displays stuffed rats hanging from traps.