The world's longest known cave system.

Stalactites and stalagmites in a beautifully lit cave.

Four glass boxes hover over 1,000 feet in the air to give visitors an unparalleled view of Chicago.

A stunning, two-tiered waterfall made famous by poets, artists and the legend of a ghost dog.

In the middle of an extremely unforgiving and desolate high desert is the most secret military facility in the world.

The popularity of Sherlock Holmes led to the creation of his fictional address, turning the orderly London street numbers askew.

A walk-in working camera obscura produces 360-degree live images of the San Francisco coast.

Each year these high desert hills are absolutely covered with poppy flowers in a surreal show of nature.

The oldest hotel in the world has been operated by the same family for over 1,300 years, even catering to samurai.

The beautiful baroque library of the Hapsburg empire.

A Hawaiian stairway to heaven—that you can't climb.

Whisper secrets in a busy station only to be heard on the other side of this acoustic arch.

The largest hot spring in the United States is, as the name suggests, a stunning show of natural color.

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

A heavenly experience, right here on Terra Firma.

An underwater city for the dead.

Carved by a waterfall in a hard-to-reach rock formation, this heart-shaped rock has inspired romantics for decades.

Behind this beachfront shop lies a spectacular, colorful sea cave with an equally colorful past.

A book collector's dream, this Toronto bookstore has the world's first "Biblio-Mat," a random book vending machine.

An abandoned stretch of highway, deteriorating next to the operational one.

These remote Florida islands have a history of sea turtles and sunken treasures, and one of the world's largest coastal brick fortresses.

An ethereal glowing blue ocean cave in Croatia.

A gargantuan crystal kingdom.

A natural gas leak provides a flickering flame beneath a waterfall.