The ruins of a 2,000-year-old Roman fishing village perched on one of the best beaches in Spain.

The rustic think-space of famed naturalist John Burroughs stands exactly as he left it.

A Spanish forest is filled with mysterious stone carvings.

The scene of the United Kingdom's most famous UFO incident, dubbed the "British Roswell."

This Nazi ruin was the site where Hitler was almost blown up by a suitcase bomb.

Built to transport German U-boats through the never-completed Masurian Canal, the locks near this Polish village are now home to a rope course.

Five miles of underground river link lake to ocean.

Settled by the Church of Jesus Christ of Latter-day Saints in 1859, this abandoned frontier town has appeared in several films.

The unusual patterns in this rock formation result from two distinct modes of weathering.

The stunningly blue waters of these beautiful caves also have a violent past.

Perhaps the most spectacular grotto along the Algarve coastline.

Caves that can't seem to quit producing the remains of prehistoric humans.

Despite violent work crews and massive delays this abandoned canal tunnel was built to last into the modern day.

A tour of underground Berlin takes you through WWII air raid shelters and tunnels used to smuggle people out of East Germany.

A southern Swedish island is home to the last ERSTA artillery battery, meant to protect the shoreline during the Cold War.

Not one, not two, but three natural bridges remain in this captivating spot post-sinkhole.

This top secret Chinese military megaproject is the world’s largest human-made tunnel structure.

Monty Python fans will recognize this abandoned mine as the Cave of the Killer Rabbit of Caerbannog.

This simple highway curve has become a comedic pilgrimage site.

This vertical pinnacle in China was the inspiration for the floating mountains in the movie “Avatar.”

An ancient capital city that dates back 3,000 years old and harbors many surprises.

Descend 2,030 years into the past in an ancient tunnel built to support Jerusalem's most famous wall.

An impressive ensemble of sculptures that survived the Soviet regime.

Above Breckenridge, a destructive mining technique sits sunken in a small pond.