In China's southernmost sansha city, the xisha islands, there is a mysterious place called the "dragon cave" by local fishermen.
The cave is so deep that it is rumored to contain huge animals.
The fishermen were afraid to approach the place and avoided it.
Later, there was a navy surveyor who hung a rope with a sounding hammer and lowered the water.
The secret of the dragon hole remains unsolved. No one knows its depth
On July 24, 2016, the sansha municipal government officially named the blue hole "yongle dragon cave" after the on-site investigation by experts.
According to the data released by the scientists, the maximum depth detected by the submersible robot is 300.89 meters.
As a result, the yongle dragon cave has been identified as the world's deepest known blue hole in the ocean.