The Yonaguni underwater monument
The account
Steps and terraces on the seafloor would be the ruins of a sunken civilization, a Japanese "Atlantis."
What investigators found
Many geologists explain the shape by the natural fracturing of sandstone into straight layers. One Japanese researcher argues for a human origin. The case remains open.
The story
In 1986, diver Kihachiro Aratake found, near the island of Yonaguni at Japan's southern tip, a striking stone formation about 25 meters down: steps, flat platforms and straight walls resembling a terraced pyramid.
Geologist Masaaki Kimura, of the University of the Ryukyus, spent years arguing that it is a human construction, submerged when sea levels rose thousands of years ago. Other geologists, such as Robert Schoch, concluded that the local sandstone naturally breaks along straight lines and angles. The monument has become a famous dive site, and the debate goes on.