Researchers investigate the newly named Sansha Yongle Blue Hole in Xisha Islands in Sansha City, South China’s Hainan Province, July 24, 2016. The almost vertical blue hole, located at 16°31′30″north latitude and 111°46′05″east longitude, measures 130 meters in diameter at the top entrance and 36 meters at the bottom, and is not connected with the ocean. It’s said to be the deepest blue hole in the world.(Photo: China News Service/Luo Yunfei)
