The Underwater Cave Nobody Could Reach for 30,000 Years

Thirty-seven meters below the sea off southern France, there is a room the water sealed shut, and for almost the entire time it has existed, no human being alive could get into it. Not because anyone hid it. Nobody buried a door or carved a warning. The ocean did it, one meter at a time, and then left whatever was inside to sit there in the dark. In 1985, a diver named Henri Cosquer swims past a gap in the rock face that should not be there. He has no idea what he's looking at. Neither does anyone else.