What are sinkholes? Are they dangerous? Sinkholes can turn a quiet pleasant canoe trip into a struggle for survival. It’s as if some great beast opens its mouth, wraps its watery tentacles around you, and pulls you deeper…and deeper… Wow! That’s too scary! Okay, what secrets do sinkholes hide? Are they as mysterious as they seem?

One of the largest underwater holes in the world is the Great Blue Hole. For a long time, people believed it was created by an ancient civilization. The thing is that it's perfectly round. That's why some people still believe it has an artificial origin and once served as storage for something mysterious… By the way, in 1971, famous researcher and traveler Jacques Cousteau went down the sinkhole. Wanna know what he discovered? Learn more about your ad choices. Visit megaphone.fm/adchoices