The Yonaguni Monument (与那国島海底地形, Yonaguni-jima Kaitei Chikei, lit. "Yonaguni Island Submarine Topography") is an underwater structure off the coast of Yonaguni, the southernmost of the Ryukyu Islands, in Japan. There is a debate about whether the site is completely natural, is a natural site that has been modified, or is a man-made artifact.