Around the world, in places as diverse as Homestead, Florida and Yonaguni, Japan stand monuments and ruins whose origins are shrouded in mystery. Nobody knows exactly why Stonehenge was built, how a set of manmade ruins came to be submerged deep in the ocean or who commissioned a giant carved granite set of post-apocalyptic instructions for rebuilding society on a remote hill in Georgia.

Monumental Instructions for the Post-Apocalypse

On a barren knoll in northeastern Georgia stands one of the world’s most bizarre and mysterious monuments. But it wasn’t created during ancient times. Known as the ‘Georgia Guidestones’, this stone structure of five 16-feet-tall, 20-ton slabs of polished granite is inscribed in eight languages – including Egyptian Hieroglyphics, Hindi and Swahili – with instructions for dazed post-apocalyptic survivors attempting to rebuild civilization. It’s oriented to track the sun’s east-west migration year-round, and has holes that allow gazers to locate the North Star. The Georgia Guidestones were commissioned by an anonymous group, whose identity remains a mystery.

Lake Michigan Stonehenge

A group of researchers using sonar to look for shipwrecks at the bottom of Lake Michigan got quite a surprise when they found what appears to be an ancient Stonehenge-like structure 40 feet beneath the surface of the water. Some of the stones are arranged in a circle and one appears to show carvings of a mastodon. The formation could be as much as 10,000 years old, which is coincident with the post-Ice Age presence of both humans and mastodons in the area. Michigan already has petroglyph sites and standing stones.

Underwater Ruins in Japan

On the southern coast of Yonaguni, Japan, lie submerged ruins estimated to be around 8,000 years old. Though some people believed that it was carved by geographic phenomena, it’s now confirmed to be man-made as the intricate stairways, carvings and right angles suggest. It was discovered in 1995 by a sport diver who strayed too far off the Okinawa shore with a camera in hand.