In the deep blue sea off Okinawa’s Yonaguni Island lies a stone structure of epic proportions. But is it natural or manmade? Mystery, history, mythology and geology all come together at this enigmatic underwater structure off Japan – the Yonaguni Monument – that raises more questions than it answers. Does this underwater structure provide evidence of a sophisticated, ancient civilisation? Or have years and years of seismic activity given way to a bizarre natural formation?

YONAGUNI, 100 KILOMETRES from Taiwan and 2,900 kilometres from Tokyo, is dotted with green sugar cane fields, tropical scrub, and grassy patches of land grazed by the tiny Yonaguni horse. With stunning lookouts, white sandy beaches and colossal rocky cliffs falling into the clear blue-green seas, the island also happens to be Japan’s westernmost inhabited place and the last in the chain of Ryukyu Islands in Okinawa prefecture. One small town, two very small villages and two sheltered harbours form the human addition to the island, while coral bommies rest in the shallow water. Benefitting from the full brunt of the Kuroshio Current, it’s known for swordfish, tuna, giant cuttlefish, barracuda and schools of hammerhead sharks that gather in the waters to breed during the winter – so ubiquitous, in fact, that divers travel from all over the world for a chance to swim with them.


But underneath the clear blue waters lies something else, a mystery of epic proportions, literally and figuratively. Yonaguni is famous for some mysterious underwater ruins called the Yonaguni Monument, and the mystery comes from the fact that nobody knows what they really are, when they were built or by whom. Their existence has led to countless debates, and neither the Japanese Agency for Cultural Affairs nor the government of Okinawa Prefecture recognises the ruins as important cultural artefacts. In fact, no government research or preservation work has been carried out on them.

Fifteen minutes away from Yonaguni’s harbour, the seas can be mildly rough with fairly strong currents, and the breaking waves look like dark, roiling storm clouds creating the perfect atmosphere for something strange and mysterious. Here, where the ruins are, the stones (sandstone and mudstone dating back to around 20 million years ago) are cleft at sharp angles and there are other shapes like arches and steps, waist-high passageways and conical borings in the rocks. The main feature, the “Monument”, is rectangular, with its top about five metres below sea level.

What is known, however, is that the ruins were discovered in 1987 by a local fisherman named Kihachiro Aratake, who happened to be diving for hammerheads  in the hope of finding a new spot to show tourists the huge sharks. Instead, he came across something even more exciting, and felt shivers up his spine as he back-rolled on top of an enormous pyramidal structure that began relatively close to the surface before its walls plunged into the deep. Aratake, who now runs his own dive centre, Sou-Wes Yonaguni, was convinced that he had discovered the remains of an ancient civilisation, and named the dive point Iseki Hanto, or “Ruins Point”, from the structure’s resemblance to an old pyramid-like temple.

Word then spread across the island, as Aratake began to seek the advice of experts. As the ruins were visited by divers more often and their structure mapped out, further discoveries were made, such as arched entrances and carvings, narrow passageways and matching obelisks that seemed perfectly aligned. Over the following years experts descended upon the site to determine whether the structure was natural or man-made. Yet to this day, it remains a great, unsolved mystery.

Read the rest of this article in 2016 Issue 3 Volume 142 of Asian Diver magazine by subscribing here or check out all of our publications here.

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