Archeologists have long believed that civilization as we define it--intelligent, tool-making, monument building, social humans--began about 5,000 years ago. But submerged beneath the waves near the Japanese island of Yonaguni is evidence that may well overturn that long-held theory. 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. HISTORY'S MYSTERIES travels to the site and plunges beneath the waves to examine the discovery, and talks to the investigators who are trying to unearth the secrets of "Japan's Mysterious Pyramids".