Yonaguni is a little island located in the far southern portion of Japan. Submerged off the coast of Yonaguni are a series of mysterious structures that appear to be giant steps carved out of the bedrock. Indeed, viewing photographs, or even diving the site and superficially inspecting the monument, it looks like we have here the side of a step pyramid, but a step pyramid covered by the ocean. How can this be? One suggestion is that in fact this is a step pyramid, and it was originally built on land a very, very long time ago. It is known that sea levels have risen substantially, by a hundred meters or more, since the end of the last glacial period about 10,000 or 12,000 years ago. Could the Yonaguni Monument be a remnant of a pre-glacial civilization that was inundated with the rising sea levels? Does Yonaguni represent the physical remains of the legendary lost continent of Mu (sometimes referred to as Lemuria, essentially the Pacific equivalent of the lost continent of Atlantis)?
If we have the remains of a very ancient human-made structure off the coast of Yonaguni, one dating back to around 8000 B.C., this would be of great interest, and of great interest to me in particular. After all, I have concluded that the Great Sphinx of Egypt dates back to a very remote period (at least 5000 B.C., and maybe even 8000 or 9000 B.C.), and I would dearly love to find other evidence of sophisticated culture, advanced civilization, and monumental stonework at this early period. With this in mind, I have visited Yonaguni on several occasions and made dozens of dives on the site (that is me with the wetsuit with yellow arms in the second photograph, using a hammer and chisel to collect underwater rock samples at Yonaguni).
As difficult as it may be for some to believe, after carefully studying the Yonaguni Monument I have to report that I do not believe it is an artificial, human-made structure. It is indeed an absolutely incredible structure, and well worth seeing, but I must conclude that, based on all of the evidence, it is primarily a natural structure. The rocks of the region break out neatly, both along horizontal and vertical planes, and naturally form the step-like appearance. This is seen both underwater and on the surface of Yonaguni.
However, if I simply state that the Yonaguni Monument is natural, I leave out part of the story. On the island is evidence of very ancient human habitation, including tombs and other structures artificially carved from the bedrock (see the accompanying photo) that I am convinced mimic, and were stylistically inspired by, the natural features of the island, including the step-like features now submerged by the ocean. Indeed, I believe that even though the Yonaguni Monument may be primarily natural (say, over 95% natural), parts may have been "touched up" by ancient humans and the ancient inhabitants of the island may have both admired and utilized the Yonaguni Monument. Analogously, we can consider the famous prehistoric cave paintings of Europe. The caves themselves are natural (although in a few places perhaps artificially enlarged), but the caves were utilized by ancient humans and the paintings on their walls and ceilings are clearly artificial productions by early humans. Although, disappointingly, the Yonaguni Monument is natural, the island itself attests to habitation by an early human population.