The Yonaguni Monument is a mysterious underwater rock formation off the coast of Yonaguni Island, Japan. Discovered in 1986, it consists of massive, layered stone structures that resemble terraces, steps, and platforms, leading to speculation about whether it is a natural geological formation or the remains of an ancient, submerged civilization. Some believe it could be evidence of a lost culture, while others argue it is the result of natural processes such as erosion. Despite ongoing debate, the Yonaguni Monument remains an enigmatic and popular dive site.