The longest navigable underground river in the United States is home to countless blind and albino animals.

This now-abandoned part of the original transcontinental railroad route provides a surreal driving and historical experience.

The remains of the iconic train crash from the movie The Fugitive can still be found rusting along the Great Smoky Railroad.

A perilous medieval road leading right into the sea.

America's only nuclear missile silo open to the public.

The last occupied troglodyte dwellings in England weren't abandoned until the 1960s.

An abandoned castle owned and ignored by Masons carries a cursed history.

This small hermitage is located along an ancient route that connected the Tiber and Rieti valleys.

A piece of the iconic wall found an unlikely new home in a Vegas bathroom.

Now overgrown, these anti-tank barriers from World War II are sometimes called "dragon's teeth."

The beautiful tunnel that ran from the lobby to Penn Station is still hidden underneath 34th Street.

Is this the most Portland place ever?

These old stone ruins in the Oregon wilderness were once bathrooms and are steeped in legends of murder.

This raised bulls-eye visible from space was the subject of an intense geologic controversy.

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

The closest thing to Mars on Earth.

A stray meteor left this picturesque hole in the Australian outback.

A lake in the middle of the tundra of Quebec is said to be the purest freshwater lake on Earth.

The meteor that sealed the fate of the dinosaurs landed at this site, one of the largest impact craters in the world.

A meteorite-bounded town in Bavaria.

Mysterious craters may have been home to an ancient cult.

One of the largest, oldest, darkest, quietest motel rooms in the world.

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

The only structure left with direct ties to the Salem witchcraft trials of 1692.