🇯🇵 Japan · Megalith
Yonaguni Monument
Geological: Early Miocene sandstone (20 Ma) formation; if artificial, claimed Jomon or earlier (10,000–2000 BCE) · Disputed – natural geology vs hypothetical Jomon / lost Pacific civilization
Submerged sandstone formation off Yonaguni Island discovered 1986 featuring stepped terraces up to 27 m high, flat surfaces and apparent right angles at 25–30 m depth, extending ~150×40 m.