The Yonaguni Monument is an underwater rock formation located off the coast of the Japanese island of Yonaguni. It is believed to be the remains of an ancient civilization, and is estimated to be around 5,000 years old. The monument consists of a series of terraces, platforms
From Wikipedia
The Yonaguni Monument , also known as the 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 100 kilometres east of Taiwan.