7 Most Bizarre Underwater Discoveries Nobody Can Explain

The underwater complex of Yonaguni has been one of Japan's great aquatic mysteries since dive tour operator Kihachiro Aratake stumbled upon it back in 1985.

This ancient structure, which is submerged off the southern coast of the Ryukyu Islands, has sparked heated debate among archaeologists and researchers, who are unable to agree whether it's man-made or a natural formation.

One school of thought is that the Yonaguni complex is all that is left of Mu, a fabled Pacific civilization said to have vanished beneath the ocean in the distant past.

The formation, which is made up of fine sandstone and mud-stone, has been referred to as Japan's Atalantis and may actually be millions of years old.