Yonaguni Mountain | Underwater Ruins

To some, it is possibly the oldest man-made structure in the world. To others, just because it looks “man-made” doesn’t mean it actually is:
the Yonaguni Monument

The Yonaguni monument   
The Yonaguni monument is a massive sunken structure, named after one of the many islands along the south coast of Japan where the underwater ruins were found. It was discovered by Japanese scuba diver Kihachiro Aratake in March 1985.

Pictures and Video
The site consists of what appears to be massive Inca-like structures and includes a face statue, an alter (or stage), “carved” steps, flat terraces, platforms and much more. Have a look at these pictures. What do you think? Man made or not?