Yonaguni Monument, Underwater rock formation near Yonaguni Island, Japan.
The Yonaguni Monument is a sandstone formation resting on the seabed off the coast of Yonaguni and extending across several levels. The structure shows surfaces that look like steps and shapes that resemble artificial working.
Kihachiro Aratake found the formation in 1986 while searching for hammerhead sharks in the waters of the Ryukyu Islands. The finding triggered a debate that continues today among archaeologists and geologists about the origin of the structures.
The site takes its name from the island where fishermen have lived off the sea for generations and now take visitors to the rocks by dive boat. Some residents see a connection to the region's ancient culture in the steps and edges, while others recognize it as a work of nature.
Divers reach the site at around 85 feet (26 meters) deep, where visibility changes with season and current. Water temperature stays between 68 and 82 degrees Fahrenheit (20 and 28 degrees Celsius) year-round, so a wetsuit is recommended.
The surfaces display lines and angles so regular that some observers want to see traces of human work in them. Others point out that sandstone can form similarly straight fractures through erosion.
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