Submerged stone structures lying just below the waters off Yonaguni Jima are actually the ruins of a Japanese Atlantis—an ancient city sunk by an earthquake about 2,000 years ago.
That's the belief of Masaaki Kimura, a marine geologist at the University of the Ryukyus in Japan who has been diving at the site to measure and map its formations for more than 15 years.
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"The largest structure looks like a complicated, monolithic, stepped pyramid that rises from a depth of 25 meters [82 feet]," said Kimura, who presented his latest theories about the site at a scientific conference in June.
There's a few photos of the underwater site and a couple comparative ones of terrestrial features. One can certainly see how they could appear man-made, but it will take far more conclusive evidence than this.