Castle and secret tunnel withstood a siege until its owner was killed by the Holy Roman Empire, while sitting on the toilet.

A miniature train-ride through Slovenia's largest cave system.

The watery entrance for condemned prisoners heading to the Tower of London is still visible along the Thames.

Daredevil repair workers can worm their way out the access hatch, loop ropes over the apex and rappel down the monument.

Less a museum than a bizarre fantasy world created by artists and engineers.

The granddaddy of all tourist traps, built on ice water, jackalopes, and a giant dinosaur.

A beautiful geyser under environmental threat.

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

An apocalyptic seismic event creates a deadly chain reaction that ends with a 6-mile long lake developing within weeks.

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

The park that the Chicago Stockyards built.

You were once able to challenge a chicken to tic-tac-toe at this park, which is now converted into the Aikman Wildlife Adventure.

Once one of the world's great cities, Cahokia was a place of religious worship, trade and mass human sacrifice before being mysteriously abandoned.

400 million-year old limestone caverns nestled in the Ozarks served as shelter and a hideout for cultures throughout North American history.

Soaring over the Niagara Whirlpool since 1916.

Niagara Falls holds a special place in Nikola Tesla's history, so they put a statue on it.

One of many reminders of Tesla's scientific contributions overlooks the falls which inspired him.

Go inside to really appreciate this 500-year-old technological masterpiece.

A series of waterfalls and pools that flow through the 'Ohe'o Gulch and into the ocean.

Victorian "Fancy Craft" Hair Wreaths and Relics.

Strange red rock formations that have been attributed to a higher power for hundreds of years.

Ancient pueblos built into the base of a natural canyon wall.

This 4,000-foot-diameter hole is touted as "the most well known, best preserved meteorite crater on Earth."

The world's largest mountain carving could fit all of Mount Rushmore inside it many times over.