Nice link. The underwater 'thing' at Graham's site is off the coast of Okinawa and would have been above water level at the end of the last Ice Age ... and it is conjectured that the site was a ruin even before it became a sumberged site, covered by the rising waters of the ice age ending.
I saw a TV show which examined this particular site and the claims being made about it; at first glance it looked like a man made site, but as the camera moved around and you were able to see the site with divers next to it giving it proper size context and proper proportions, it became obvious that this was a natural site. The rock simply broke off in layers which made portions of it look like steps, but the steps were uneven and did not lead anywhere. There was no evidence of any marks made by human tools. There was nothing to indicate that it was man made; it is, in fact, a natural rock formation.
I'm not saying that there are not ancient pre-historical sites to be found underwater, only that this particular site is not one of them.
Care to revise or extend your remarks? :^)