In the 1980s, local divers discovered a striking underwater rock formation off the southernmost point of the island. This so-called Yonaguni Pyramid has staircase-like terraces with flat sides and sharp corners.
In 1985, Kihachiro Aratake, a diver from Japan, was diving in the waters off the Southern shore of Yonaguni island and discovered something unusual. Upon inspection, it appeared to be a man-made, terraced structure. Believing he had discovered a sunken city, Aratake announced his discovery, but there was not much interest. Later, in 1996, Professor Masaaki Kimura , a professor at the University of the Ryukyus, began to survey the structure. While Kimura maintains that the site is evidence for an advanced prehistoric civilization, others argued that the structure was the result of natural phenomena. Research in the ensuing years has arrived at a consensus that the structure is indeed a man made monolith carved from a natural formation.
The sea off Yonaguni is a popular diving location during the winter months due to its large population of hammerhead sharks. In 1987, while looking for a good place to observe the sharks, Kihachiro Aratake, a director of the Yonaguni-Cho Tourism Association, noticed some singular seabed formations resembling architectonic structures. Shortly there after, a group of scientists directed by Masaaki Kimura of the University of the Ryukyus visited the formations. Kimura is a strong advocate of the view that the formations are manmade
The formation has since become a relatively popular attraction for divers, in spite of the strong currents. In 1997, Japanese industrialist Yasuo Watanabe sponsored an informal expedition comprising writers John Anthony West and Graham Hancock, photographer Santha Faiia, geologist Robert Schoch, a few sport divers and instructors, and a shooting crew for British Channel 4 and Discovery Channel. Another notable visitor was freediver Jacques Mayol, who wrote a book on his dives at Yonaguni. A plaque in his honor was fixed to the undersea formations after his suicide in 2001.