In 1987, a diver made an amazing discovery while exploring the coast of the Ryukyu Islands in southern Japan. 25 meters below the surface, he saw almost perfectly carved steps.

“Do you know the sensation of gooseberry? My hair is gone, it’s overgrown,” recalls Kihachiro Aratte, who was looking for a diving spot when he came across the structure near Yonaguni Island, part of the archipelago.

Known today as the Yonaguni Monument, this colossal structure is reminiscent of a 50-meter-long and 20-meter-wide rectangular pyramid, the world’s most spectacular underwater formation.

“I was very touched when I found it,” he says. “I know it will become a treasure on Yonaguni Island.”

After Arattic discovered this structure, a team of scientists led by Masaki Kimura, a geologist at the University of Ryukyu in Japan, began research on the formation of submerged rock.

It is thought to be over 10,000 years old. But its origins divide opinions.

“I think it’s very difficult to explain that its origin is completely natural because there is so much evidence of human influence on the structure,” Kimura says.

In this line, there are those who believe that this structure is a remnant of a civilization that has been lost for a long time in the Pacific, probably built by the prehistoric Jomon people of Japan who lived on these islands around 12,000 BC.

The nickname “Atlantis of Japan” is not for nothing.

“The spiral staircase makes me believe it is man-made,” Aratte points out.

Although the narrow sections and arch entrances are 90 degrees parallel, most geologists say the Yonaguni monument is an unusual natural formation – especially since the structure is connected to a large rock.

“When I first saw it, I immediately realized that the formations were similar to those on land,” says Takayuki Ogata, a geoscientist at Rukyu University.

“I ‘ve never seen constant shapes from land to sea bottom, which really fascinated me.”

Since the monument is located in an earthquake prone area, well-defined layers of the structure are believed to have formed gradually.

Makoto Otsubo, a geologist at Rukyu University, recalls that symmetry forms and formations can be found in nature.

“It can be explained by other landscapes that are similarly formed,” he explains.

This is the case with the Giants Causeway in Northern Ireland, where thousands of interconnected basalt columns were formed by volcanic eruption millions of years ago.

Whatever the origin, the discovery of the Yonaguni Monument fascinated visitors, and professional diving expert Kenzo Watanabe tried to plan a trip to the island without wasting time.

“There were rumors that if it was turned into an archeological site, we would not be able to drown there anymore, so I decided to go as soon as possible,” he reveals.

“After seeing (the monument), I think there’s no way man could build it, especially on those flat surfaces. It’s really impressive, with different surfaces and symmetrical shapes. I think it’s not natural.”

While the story of the monument’s mythological origins may not be true, it will continue to appeal to those lucky enough to drown there – and to get a closer look at this unique geological phenomenon.