“The Blue Hole is made of a complex system of caves that once formed on dry land. It is proof of how oceans can rise quickly and catastrophically, he wrote at the time.

That’s 480 feet deeper than the previous record holder, the Sansha Yongle Blue Hole, aka the Dragon Hole, in the South China Sea, which measures 990 feet to the bottom.

It's a limestone cave, to be exact. The Great Blue Hole contains stalactites and stalagmites below the surface, some 40 feet in length. And as with any good cave, more mysteries lie within.

A team including Virgin billionaire Richard Branson has returned from the bottom of Belize’s Great Blue Hole with exciting findings. Learn what’s down below 400 feet of Caribbean Sea.

Great Blue Hole: Cousteau and Branson to Map World's Largest Sinkhole. Two Boeing 747s could fit inside, with room to spare. by Tiffany Jeung ...

"After spotting this deep blue hole on google maps we decided to head far offshore, out further than our normal Reef trips to see what dwelled within," he wrote.

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