Answer: Mexico
Notes: Scientists continue to explore Mexico's Taam Ja' Blue Hole in Chetumal Bay, hinting at a connection to a complex network of underwater caves. Blue holes, like Taam Ja', are sinkholes formed by the dissolution of soluble rock, such as limestone. Taam Ja' is the world's deepest known underwater sinkhole, plunging at least 1,380 feet below sea level. It surpasses the previous record holder, the Sansha Yongle Blue Hole, by 390 feet.
