It could be a random pile of rocks, or it could be the Asian Atlantis. Located just off the shores of Yonaguni, one of Japan's most southerly islands, the Yonaguni Monument is a vast collection of stone structures believed by some to be the sunken remnants of an ancient civilization. At first glance, Yonaguni's human origins seems obvious: The site is composed of right-angled stone walls topped by a massive stone pyramid. Japanese marine geologist Masaaki Kimura, who has studied Yonaguni for 15 years, maintains the sprawling site once held a stadium, five temples, a triumphal arch and a castle [source: Ryall]. In certain spots, Kimura says, stones are nicked by what appear to be quarry marks.
Skeptics maintain that the monument's resemblance to an ancient city is merely a coincidence. Sandstone naturally breaks along straight lines -- especially in earthquake zones -- and could have easily formed the monument. To look at maps of the site, Yonaguni certainly doesn't seem like a very welcoming city. Some of the monument's high terraces appear to be joined by "staircases" with steps that are up to a meter high. Peculiar for an archaeological site, the Monument has also been found to contain no tools or pottery.
Boston University professor Robert Schoch (who also theorizes that Easter Island was built by ancient giants) thinks that Yonaguni may be a mixture of both natural and manmade structures. Before the monument was buried by a massive tsunami, ancient humans may have lived among its formations, says Schoch. And just as prehistoric humans decorated the caves of France, the residents of the Yonaguni Monument "spruced up" the place with some carvings and tombs [source: Schoch]. So far, the Japanese government isn't buying any of this. More than 20 years after it was discovered, state officials have yet to send an official expedition to the site.