The final challenge of The Witness is bullshit. It's a bunch of puzzles, the whole collection timed and randomized. You start the challenge, by turning on music. You have until the music ends, to do all of the puzzles. If you don't make it, you have to restart. The time limit is doable, but far from generous. Basically, you don't have time to think much about the puzzles. There is a bit of time, but there should be more.
You also can't learn a puzzle, and then just do it again next time. The puzzles are randomized. And I think I found some that are unsolvable? Maybe? I could have sworn that some have no solution, but being under time pressure doesn't help with the concentration.
Speaking of unsolvable - part of the challenge are three screens, of which only one shows a solvable puzzle. The other two you see at the same time are unsolvable, by design. You have to find the one that is doable. This happens two times in a row.
An early puzzle of the challenge shows you a map. You actually have to remember it, aside from making a route through, together with two dots. Because near the end of the challenge, there is a labyrinth with hidden walls, jumping out when you get near them. Sure, you can just run through, but there isn't enough time for that. You need the map from earlier, including the two dots you had to collect. Because the dots are the places where you find two more puzzles. Which weren't super hard, but also not trivial. One time, after solving the puzzle, I was completely disoriented, and had to restart for that reason.
It's just so stupid. At this point, you aren't really solvign logic puzzles. The puzzles are simple, because you don't have time to think. It's the opposite of why I like to play puzzle games. There is no time pressure, they are relaxing, and so on. This part is everything, but that.
I still beat it, because you will do so, if you just get easy puzzles. That's all there is to it, really. It just feels so pointless.
Anyway, the cave system still has some regular puzzles, which should be a good amount of the ~40 I'm still missing.
Also, I used a guide for that puzzle on the wrecked ship. I don't feel bad at all.