interesting reading Wikipedia The Yonaguni Monument 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.[1] These claims have been described as pseudoarchaeological.[2] Neither the Japanese Agency for Cultural Affairs nor the government of Okinawa Prefecture recognise the features as important cultural artifacts and neither government agency has carried out research or preservation work on the site.[3]

Lots of great photos on all types of sites (diving & pseudoarchaeological)