by Dr. Colette M. Dowell 
News Flash ! © 1997

Excerpt:

Yonaguni Island belongs to a chain of islands known as the Ryuku Islands, which stretch Southwest from Japan towards the mainland of China. Yonaguni is the last of the islands of this chain and is only 30 miles from Taiwan.

Ten years ago while looking for interesting under-water sites to dive near Yonaguni, scuba diving instructor Kihachiro Aratake, discovered an amazing under-water construct 20 feet below the surface of the water. The construct is defined as being "as if terraced into the side of a mountain," resembling a grand stand for Sea Gods, or somewhat like an amphitheater with its huge steps and blocks of stone. The construct's 250-foot base lies 100 feet below the ocean's surface and rises to a height of 80 feet. 

SOURCE: Dr. Robert M. Schoch, Ph.D.

Terraces and steps: prehistoric rock-hewn structures at Sacsayhuaman and nearby Qenko in the high Andes mountains of Peru

This Diving Site has a very good collection of sources and photos of Yonaguni
http://www.divejapan.com/yonaguni_monument.htm

Japan's Mysterious Submerged Stone Structures:
New evidence suggests they may have been used by Man
by Laura Lee

Excerpt:

YONAGUNI: The ancient underwater pyramid structure off the coast of Yonaguni-jima, Japan

Man-made, made by Nature, or did humankind finish what Nature started? These enigmatic, sunken stone structures off Okinawa, Japan, located 60 to 100 feet beneath the ocean surface, have the Japanese wondering if their homeland was once part of the lost continent of Mu.

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)

SOURCE: http://www.lauralee.com/japan.htm

A small but persuasive number of scholars and scientists have long thought that "advanced" societies may have existed as long as 10,000 years ago. Their theories, however well reasoned and defended, have been hamstrung by a lack of evidence. But recent discoveries of man-made artifacts on the Pacific seafloor may well prove to be the smoking gun that will propel this alternative view of civilization to prominence". 

SOURCE: Morien Institute

http://www.eichhorn.ws/html/body_grenzwissensch..htm