This whimsical castle of grottoes was the labor of love of a French postman, and one of the greatest achievements of outsider architecture.

The original home of the Lego has a huge amusement park dedicated to the iconic plastic toy.

Micro-nation based around a nine-story high illegally built tower.

America's most famous piece of self-built architecture.

A botanic garden full of trees twisted into fantastic shapes and positions.

Naturally protected city carved from a rock face.

Roman ruins top white travertine terraces formed by ancient hot springs.

Roman ruins, natural methane fires and a lovely beach.

A naturally beautiful, seemingly bottomless deep blue spring.

A spectacular cave and a beguiling lake.

Monasteries on rock pillars, once accessible only by frayed ropes.

Cretean quarry suggests real-life site for ancient Greek myth of the man-eating Minotaur in his labyrinth.

A breathtaking array of ancient Pueblo structures and artifacts counterintuitively preserved by neglect.

Stone Age solar temple is aligned with the sun on each equinox and solstice.

Ancient mysterious ruts carved in the bedrock.

The Jesus tree of Malta bears a striking resemblance to Christ on the cross.

An abandoned set from the 1980 film "Popeye," claimed and repurposed as a theme park by creative locals.

An abused and forgotten metropolis, abandoned for centuries.

This sculpture by artist Fritz Keonig survived the 9/11 attacks and now stands as a monument to the victims.

These medieval skyscrapers dominate the skyline of this small Tuscan town.

Four glass boxes hover over 1,000 feet in the air to give visitors an unparalleled view of Chicago.

An unoccupied lighthouse encased in layers of ice from the waters of Lake Erie.

Little island known for its massive beachfront "flowerpot" pillars.

This Niagara Falls tourist trap is a world bright with neon and curiosities that will inspire love, hate, or a mixture of both.