Stone terraces, right angled block and walls, and stone circles encompassing hexagonal columns look intriguingly, if not conclusively, man made. A few more clues: an encircling road, what might be post holes supported long-gone wooden structures, what look like cut steps, and castles with similar archietecture located nearby and still on land. (see photos; link at end of this article)
The two sites that are getting the most attention: near the city of Naha is Okinawa is what looks like a wall, with a coral encrusted right angled block. Another, just off the southern end of the tiny island of Yonaguni, the southernmost island of Japan, is an extensive site, with five irregular layers that look like ceremonial, terraced platforms. There are eight anomalous, underwater sites found to date.