we're not designed to breathe underwater. >> simon: during her career as a free diver, tanya streetereeper than any man. the key to her success, she says, is her ability to equalize the pressure underwater so her eardrums don't burst. >> streeter: as you dive, the... the pressure of the weight of water around you increases. and it pushes your eardrums in and in and in, and you have to push air into the eustachian tubes to be able to pop the eardrums out to equalize that pressure. i mean, it... it hurts. i've described it as an elephant sitting on my chest, stabbing hot pokers in my eardrums. >> simon: nobody would choose to do that. >> streeter: no. but, you know, you sort of find yourself there on... at that point on your journey, and realize that that's what you signed up for. so, it... it's all par for the course. ♪ ♪ >> simon: tanya and other free divers come to the blue hole because it's the perfect place to dive. it's in the remotest part of the bahamas, called long island. christopher columbus put it on the map in 1492, but you'll have trouble finding it on any tourist map toda