There is an underwater structure off the coast of Japan that appears to be earthworks created by an unknown civilization. The “Japanese Atlantis” has been covered in Graham Hancock’s book Underworld and more recently by the History channel’s Ancient Astronauts documentary series. The key fact about the site is that it is far below sea level now and would not of been above the water level for a very long time and might have been underwater for 10000 years or more. At that time, it would have been connected to the Asian mainland and of course we have no information about sophisticated cultures that might have been responsible for such a creation.
Some experts argue that structures could be natural formations. What makes it difficult is that there are existing artificial earthworks above the sea level in Japan, like the ancient castles in Okinawa and ancient grave sites, so it is known that ancient peoples have created such structures. At the same time, the ones at Yonaguni have been underwater for so long the erosion makes it hard to know for sure. The complex mix of strange structures and arrangements in such close proximity give confidence to the proponents of the man-made possibility.
The important question that the site presents is – Is the bulk of the history of human civilization lost? One theory proposed in Gaham Hancock’s books and others is that, when the end of the last Ice Age released tremendous amounts of water and raised sea levels, it covered up a good portion of the world’s ancient cities and creations, like Yonaguni.