It's my understanding that this is done all over the world but as someone that has tried it, I can say that I don't really have what it takes. Mine wasn't even in the open sea either. It was just an ice-plunge cafe where they have the units available for you to rent. It's actually quite expensive.

you are meant to go in there for i think it was 3 minutes but I didn't even make it to 20 seconds.. haha. I don't know how someone could get used to this but apparently a lot of people do.

I can't tell from your writeup, did you actually take the plunge yourself or are you just intrigued by it?