For two weeks every June, fireflies in the Smoky Mountains perform an astonishing light show.

This eccentrically decorated palace is replete with grottoes, fountains, tunnels, and caves.

An ancient and majestic fortress that played an integral role in Portugal's road to independence.

Morocco’s modern capital was once a haven for Barbary pirates, who went so far as to establish a republic of their own.

An awe-inspiring mosque in Morocco with one of the tallest minarets in the world.

Deep underground, the rusting remains of a German water pumping station from World War II.

This was the second largest mercury mine in the world and one of the oldest preserved mine complexes in Europe.

The "dragon babies" of southeastern Europe.

Martin Bricelj Baraga's monolithic sculpture measures the blueness of the sky, and changes color to match it.

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

This one-time health resort was used by aristocrats around the world.

This massive subterranean fissure is known as the "underground Grand Canyon."

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

Japanese gardens dedicated to the Japanese farmer that refused to throw in the trowel.

An oddity shop inspired by the history of the circus.

St Bernard de Clairvaux Episcopal Church, better known as one of the oldest European buildings in the Western Hemisphere.

The sign that drew attention to a young boy's cucumber stand is now the name of his fruit superstore.

12,000 sq. ft. museum tracing erotic art from antiquity to modern times.

Located within a historic park, the beacon is the oldest standing structure in Miami.

A perfect circle of twenty-four mysterious holes dates back to prehistoric time.

A mysterious castle built as a monument to lost love.

Former villa and estate of James Deering developed to preserve native tropical forests.

This historic New Orleans cemetery is the final resting place of members of the Independent Order of Odd Fellows.

In 2010, Nicolas Cage purchased two plots in this cemetery using one to construct this strange pyramid mausoleum.