I was browsing around and ran across this. I like finding things I've never heard of before and that was the case here. It is speculated that for this construct to be above water, it would have been in the Ice Age some 8000 years B.C! Current thinking is that mankind was a bunch of rock apes sitting around in caves at that time, grunting at stuff and scratching their arses. But if this discovery off the Japanese coast is to be believed, it could point to a sophisticated civilization that was lost to the ages.

Maybe someone has some more information?