This is a video of freediver Petr Kapoun swimming under the frozen surface of Lake Milada in the Czech Republic. If I were him I probably would have panicked and drowned, except wait no I wouldn't have because I would never go ice swimming in the first place because I'm not a crazy person. I had to put on two coats and a scarf just to watch this video long enough to make a gif.
Keep going for the video.
Thanks to K Diddie, who agrees somebody sould do a volcano next.