BBC – Travel – Japan’s mysterious underwater ‘city’

Below the waves off the coast of Japan’s Ryukyu Islands, a series of curious pyramid-like formations have captivated divers and geologists since the site’s discovery in 1987.
In 1987, a local diver exploring off the coast of Japan’s southern Ryukyu Islands stumbled across a startling discovery. Twenty-five metres below the surface, he spotted a series of almost perfectly carved steps with straight edges. Known today as the Yonaguni Monument , this massive 50m-long-by-20m-wide behemoth is one of the world’s most unusual underwater sites.
Nicknamed “Japan’s Atlantis”, the rectangular, stacked pyramid-like monument is believed to be more than 10,000 years old. Some think it’s all that remains of a long-lost Pacific civilisation, possibly built by Japan’s prehistoric Jomon people who inhabited these islands as early as 12000 BC. Others say that the site resembles natural formations elsewhere around the world with distinctly defined edges and flat surfaces, such as Northern Ireland’s Giant’s Causeway , whose thousands of interlocking basalt columns were formed by a volcanic eruption millions of years ago.
This media cannot be played on your device.
Despite Yonaguni’s narrow passageways, arched entrances and seemingly parallel 90-degree angles, the unusual formations are largely believed to be natural rather than man-made – particularly since the structure is attached to a larger rock mass. The site’s well-defined layers are also likely to have gradually formed due to the site’s position in an earthquake-prone area.
Although the monument’s mythical origin story might be untrue, it will likely continue to fascinate those lucky enough to dive here and get up-close to this unique geological phenomenon.
(Video by Naotomo Umewaka , text by Yasmin El- Beih )
This video is part of BBC Reel’s World of Wonder playlist.
Join more than three million BBC Travel fans by liking us on Facebook , or follow us on Twitter and Instagram .
If you liked this story, sign up for the weekly bbc.com features newsletter called “The Essential List”. A handpicked selection of stories from BBC Future, Culture, Worklife and Travel, delivered to your inbox every Friday.