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. These claims have been described as pseudoarchaeological. 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.

The formations are located below Arakawabana cliff which is the southern tip of Yonaguni island, with its main face oriented south-southeast. 

It is composed of medium to very fine sandstones and mudstones of the Lower Miocene Yaeyama Group believed to have been deposited about 20 million years ago. Most of the rocks in the formations are connected to the underlying rock mass (as opposed to being assembled out of freestanding rocks).

According to en.wikipedia