This giant urban staircase was built to keep the city's brave fighting men from getting waylaid in the red light district.

This sprawling Belgian fort was once thought of as impenetrable but now it is simply an abandoned relic.

A little sculpture with a large wardrobe.

A Belgian self-built tower inspired by the Bible and ancient civilizations.

A flooded Mexican cave that hides a river beneath the water.

One man's fulfilled dream of living on an artificial island made of recycled plastic bottles.

No telescopes, no power, no gift shop: The Observatory of Chichen Itza, one of the world's oldest observatories, takes astronomy back to basics.

Every equinox this Maya pyramid puts on a spooky ancient light show.

Creek water that starts here has a 50/50 chance of ending up in the Atlantic or the Pacific.

One of nature's most well-scheduled phenomenons resides in Wyoming's Yellowstone National Park.

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

A beautiful geyser under environmental threat.

A museum dedicated to the history and exploration of both popular music and science fiction.

The largest island on the great salt lake is home to curious creatures and strange stories.

Giant, natural amphitheaters made of delicate geological formations called "hoodoos."

The ancient dwellings of the Puebloans, located in the cliffs of majestic mesas.

A modern day curiosity cabinet.

Standing in a state of "arrested decay," this ghost town allows for a detailed peek into Gold Rush life in an unusually harsh climate.

Explore 10 acres of environmental sculptures.

Aqueducts have dramatically changed this old lake, now home to tufa towers and its very own species of tiny brine shrimp.

America's most famous piece of self-built architecture.

A multi-storied adobe complex has been inhabited for more than a thousand years.