This is one off the craziest things we've EVER seen -- a 54-year-old freediver cut a hole in a frozen lake in the Czech Republic and swam under a sheet of ice ... IN SPEEDOS!!!
The dude behind the stunt is Petr Kapoun -- and after watching this guy handle the cold, he looks like he could be part of the White Walkers from "Game of Thrones."
Dude put a yellow string above the solid ice at Lake Milada in January to guide him along during his swim ... and it worked. He was able to get from frozen point A to frozen point B without a problem.