An unusual slot canyon in the Aztec/Navajo Sandstone has a cross-section like an inverted old-fashioned keyhole.

A secret fresh water spring for animals and humans alike hidden along the most famous road in the United States.

The natural hot spring that was integral to the creation of Canada's first national park.

A stone troll guards the hike that leads to this waterfall.

An engineering error ensured this cavernous 350-foot-long subterranean thoroughfare was never used as intended.

Icelandic folklore says this giant boulder was ripped from the mountains and placed at its current location, where it became home to elves.

A 63-foot-tall swinging ball hypnotizes passersby, and proves to any remaining doubters that the Earth is spinning.

These ancient sunken lanes were naturally tunneled into the soft ground by countless footsteps.

Northern Ireland's Brobdingnagian stepping stones.

The granddaddy of English geoglyphs dates back to the late Bronze Age.

The last inhabitants of one of the U.K.'s most remote islands were evacuated in 1930.

The largest stone moai on Rapa Nui.

The intricate stonework of Machu Picchu serves as a testament to Incan engineers.