I've never done a Hell Week, but I can imagine it's probably not a whole lot different than a week's worth of Crucible.
54 hours of basically no time to eat, almost no sleep, physical and mental challenges, and them trying to break you down and make you quit.
It was about 5 F when I went through mine. They had to literally break the ice on the creeks for us to crawl through, and we weren't allowed to wear any warming layers or gloves/watch caps, and that shit was rough.
This video shows most of the challenges, with none of the extra bullshit that they're not allowed to put on camera.

9/10, would absolutely do again.