The Yonaguni Monument

Professor Masaaki Kimura 

Professor Kimura has identified terraces with stairs and drainage fixings, areas for spiritual worship, a gusuku (castle) type structure, and a stadium. 

The Yonaguni Monument suggests that Lewchewan society thrived at an early date in human history, which likely helped to influence Lewchew's advanced status in spite of its relatively small and isolated geographic location. This also helps to explain why ancient Chinese scholars by at least the Zhou Dynasty knew of Lewchew, and considered them to be an advanced civilization that held the secret to immortality. 

The advance society at such an early date in human history, along with its demise via ocean submersion, has led some to believe this could be the legendary lost continent of Mu or Atlantis.