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

The largest earthwork effigy in the world.

Native Americans built this circle of stones, which was used to predict astronomical events.

Mysterious ancient boulder carved with petroglyphs in the mountains of Western North Carolina.

Some of the tallest ancient American ruins continue to inspire awe and curiosity.

In this historic region, homes and churches are carved into ancient volcanic rock formations.

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

Stockholm's deepest subway station is also a stunning ecological wonder.

Though strikingly beautiful, Seattle's other railway station is now largely forgotten.

The walls of America's oldest masonry fort famously "swallowed" cannonballs.

Icelandic settlement in Manitoba established in 1875.

This spectacular track has run continuously since 1882.

The narrow passages will challenge even the bravest driver.

This magnificent 18th-century hall consists of a maze of nearly a thousand interconnected passages.

An abandoned railroad tunnel is now filled with bioluminescent bugs.

A collision of human error and natural geothermal pressure created this rainbow-colored geologic wonder.

This colorful palace is an oasis of calm amid the hustle and bustle of the Buriganga riverfront.

A girls' boarding school inspired by the Chicago World's Fair, once abandoned, now restored to strange and scenic glory.

Step into a cartoon at this Seoul café that aims to evoke a two-dimensional scene.

A breathtaking flower tunnel bursts with beautiful golden blossoms.

The world's largest bamboo labyrinth is a living demonstration of the plant’s immense potential.

An archival collection of over 2,200 case studies which includes human brain specimens and tumor specimens.

The oldest arboretum on the Dalmatian coast doubles as the gardens of Kings Landing in "Game of Thrones."

This quaint Italian town keeps losing ground as the sides of its plateau slowly erode.