The Yonaguni underwater 'monument'
In 1986 a dive operator found stepped terraces of rock off Yonaguni, Japan's westernmost island; geologist Masaaki Kimura argued they are a sunken man-made structure.
1986 CE · 24.43, 123.01 · status: disputed
The account
The formation has flat platforms, sharp angles and what look like steps and channels. Kimura linked it to a lost culture drowned when sea levels rose, and writers tied it to Mu and Atlantis legends.
The sceptical view
Most geologists explain it as Miocene sandstone that naturally splits along flat bedding planes and vertical joints, worn by currents; no tools, writing or artifacts have been found.
The researched reading
A striking undersea rock formation that most geologists explain by how sandstone fractures. The case for a sunken city rests on shapes, not on artefacts.
| Explanation | Weight | Why |
|---|---|---|
| A known natural phenomenon | 50% | The "steps" and "walls" follow the bedding planes and vertical joints of Miocene sandstone, which splits naturally into flat slabs and right angles; similar formations stand on the island’s coast. No tools, carvings or debris have been found. |
| Undetermined | 28% | The share a generic explanation had beyond what has been shown for this case: it fits many cases like this one, but has not been demonstrated for this one. |
| A cultural story | 8% | Links to Mu and Atlantis come from popular literature, not from evidence on the site. |
| Perception, memory or mind | 6% | Pareidolia makes natural angles look built; Kimura’s "faces" and "roads" are interpretation. |
| Something in the surroundings | 4% | Some human modification of natural rock (quarrying when sea level was lower) has been suggested, but not shown. |
| A hoax or fabrication | 2% | No one has faked the formation; the dispute is about interpretation. |
| Genuinely anomalous | 2% | Even a man-made origin would be an archaeological surprise, not something science cannot explain. |
Official position: No official recognition as a cultural site; Japanese authorities do not list it as an archaeological monument.