Simply Scuba looks at one of Japans biggest ocean mysteries... The Yonaguni Monument (与那国島海底地形), also known as "Yonaguni (Island) Submarine Ruins" is a submerged rock formation off the coast of Yonaguni, the southernmost of the Ryukyu Islands, in Japan. It lies approximately a hundred kilometres east of Taiwan. Marine geologist Masaaki Kimura claims that the formations are man-made stepped monoliths. These claims have been described as pseudoarchaeological. Neither the Japanese Agency for Cultural Affairs nor the government of Okinawa Prefecture recognises the features as important cultural artefacts and neither government agency has carried out research or preservation work on the site.