A towering baroque basilica jutting out of the French countryside.

New Orleans' famous cemetery, located on the site of a former race track.

The site of one of history's most indelible and horrific tragedies.

The Cathedral of St. Ambrose has been hiding a special parishioner within its walls.

A wunderkammer hidden on the top floor of the Hartford statehouse.

A mining town once rife with murderous disputes over its copious treasures now creates income as a popular spot for photo shoots.

The "World's Largest Underground Business Complex," a 55,000,000-square-foot city underneath Missouri.

The United States's largest hand-dug well is topped with a state-of-the-art museum.

The kind of mixed-up place that drives archaeologists crazy.

The underground sanctuary of a mysterious ancient cult.

Ancient Greek oracle of the dead.

Nationwide network of co-ownership underground catastrophe shelters.

A nuclear bunker built to shelter the politicians and important people of Scotland in case of nuclear attack.

An unrealized dream to wirelessly electrify the entire Earth.

Explore the largest pure gypsum deposit in the world, and go dune sledding while you're at it.

"Only the devil could play golf here."

A geological mystery on Camelback Mountain.

Astonishing rock formations dot the Brimham Moor landscape.

The lake that fills and empties itself at random.

The last fully functional fortress of Germany's World War II Atlantikwall.

Underground monastery and fortress.

The largest of London's subterranean rivers and once a mad, bad center of London life.

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

Man-made cave with enigmatic carvings, some say made by the Knights Templar themselves.