This is an underwater structure built about 80 feet underwater off the coast of the southern Japanese island of Anami Oshima.
Considering no one had ever encountered anything like it, diver and underwater photographer Yoji Ookata
was at a loss to explain what had built the circular, repeating, and clearly geometric structure. The architects of this feat of underwater engineering were discovered by Japanese broadcaster NHK,
and the answer to what built the six and a half foot wide structure
is at once mundane and really impressive.