Forty years ago, a routine diving expedition off the remote Japanese island of Yonaguni turned into one of the most controversial archaeological debates in modern history. What diver Kihachiro Aratake discovered beneath the crystal-clear waters of southwest Japan has since been described as everything from a lost city to a geological illusion. As reported by Times UK, the debate over this underwater formation—known as the Yonaguni Monument—has only deepened with time, drawing in scientists, theorists and explorers from around the world.
Aratake, then a diving instructor searching for new tourist sites, recalls the moment he first saw the structure in 1986. Descending into the sea near Yonaguni, a small island close to Taiwan, he says he was struck by the sight of vast stone formations with sharply defined edges and geometric precision. To him, it resembled an ancient city hidden beneath the waves. He compared the scene to Machu Picchu, describing terraces, steps and flat platforms that appeared almost deliberately constructed.
The structure extends across hundreds of metres and includes features that appear unusually ordered for a natural formation. Flat surfaces intersect at near-perfect right angles, while tunnel-like passages cut through the rock. Two large openings even resemble eye-like shapes. Convinced he had stumbled upon something extraordinary, Aratake and his team initially kept the discovery secret, conducting repeated dives to understand what they were seeing.
For many, the most compelling interpretation is that the Yonaguni Monument is the remains of a lost civilisation. This theory was famously advanced by Masaaki Kimura, a geologist from the University of the Ryukyus, who became one of the earliest academic figures to study the site. After extensive underwater surveys, Kimura argued that the formation was not natural but man-made, potentially dating back around 10,000 years.
Kimura’s interpretation was bold. He suggested that the structure included pyramids, roads, temples and even a stadium-like space with seating areas. He claimed to have identified stone tools and carvings resembling animals. In his view, the site could be linked to the mythical lost continent of Mu, a Pacific equivalent of Atlantis that has long been dismissed by mainstream historians as fiction.
The idea quickly attracted attention beyond Japan. Writers and researchers associated with alternative archaeology, including British author Graham Hancock, visited the site and promoted the possibility of an advanced ancient civilisation existing in the region. For supporters of this theory, Yonaguni represented potential evidence of human history far older and more sophisticated than traditionally accepted.
However, the scientific consensus has increasingly moved in the opposite direction. Geologists who studied the formation, including Robert Schoch, argue that the monument is the result of natural processes rather than human activity. Schoch noted that the rock is sandstone, which naturally fractures along straight lines. Earthquakes in the region further encourage these patterns, creating angular shapes that can appear artificially constructed when viewed underwater.
He also pointed out that marine growth, including algae and sediment, can exaggerate the appearance of geometric precision. What looks like carefully carved steps or platforms may in fact be natural rock formations shaped over millennia by erosion, tectonic activity and ocean currents. While Schoch did not entirely rule out minor human modification, he concluded that the structure is overwhelmingly the product of geological forces.
Despite this scientific rebuttal, the debate has never fully disappeared. The Yonaguni Monument continues to attract divers, tourists and researchers who are drawn as much by its mystery as by its appearance. For many visitors, the question of origin is less important than the experience itself. Whether ancient city or natural formation, the site offers an unusual and striking underwater landscape.
Aratake himself has embraced the ambiguity. Now in his late seventies, he still runs a diving shop on Yonaguni and continues to guide visitors to the site. He has published his own book featuring underwater photographs of the formation, many of which he claims have been used by visiting academics without proper credit. Yet he remains unconcerned about the ongoing dispute.
In his view, the uncertainty is part of the monument’s appeal. He notes that even experts who have studied the site extensively cannot agree on its origin. While some insist it is a man-made relic of an ancient civilisation, others see it as a natural geological structure. Aratake believes the disagreement is unlikely to be resolved anytime soon, and he finds a certain enjoyment in the ongoing debate.
The controversy surrounding Yonaguni reflects a broader tension between scientific explanation and human imagination. The idea of a lost continent such as Mu or an underwater Atlantis continues to captivate public interest, even in the face of geological evidence. Such narratives speak to a desire to uncover forgotten histories and challenge established timelines of human development.
At the same time, the scientific perspective highlights the complexity of natural processes that can produce forms resembling human construction. The Yonaguni Monument sits at the intersection of these two interpretations, where perception and geology collide. What appears to one observer as deliberate architecture may, to another, be the result of tectonic forces acting over thousands of years.
Over the decades, the site has become less about proving a definitive answer and more about exploring how humans interpret the unknown. Its allure lies not only in what it might be, but in what people hope it could be. For some, it is a lost city waiting to be rediscovered. For others, it is a reminder that nature itself can create patterns that mimic human design with uncanny precision.
As Times UK notes, the Yonaguni Monument remains unresolved and perhaps unresolvable. It continues to draw interest precisely because it resists simple classification. Whether it is the remains of a forgotten civilisation or a remarkable natural formation, it stands as a powerful symbol of mystery beneath the sea.
For Aratake, that ambiguity is part of its enduring value. He is not troubled by the lack of consensus. Instead, he views it as a source of fascination that keeps people coming back. In a world that increasingly demands clear answers, Yonaguni offers something different: a place where certainty dissolves into the deep blue, and where the boundary between myth and science remains as fluid as the ocean itself.
