done anything with those monoliths, and I've only got 3 of the videos, and found 1 audio log.

Finally started doing some of the monolith stuff - weird that I'd not figured that out at until now. I'd seen some of the patterns in the environment but just never thought to try drawing directly on them.

Started doing the caverns section behind the secret door near the end. Got to some random timed puzzle which I guess is the final trophy, and, well, it's not much fun. I know exactly what needs doing now, but it seems a case of trying repeatedly until I get lucky with the puzzles. That bit running around a room with shutters popping up looking for those arrow puzzles in particular is just annoying, and just a complete fluke if you find them in time. Not worth the bother for me.

you might be onto something there
Although I hope you've got a better memory than me for it!

506 panels +19. Plenty more to find, but I think that's enough for now.

Have you found the box that looks like it should contain another pattern to activate a movie in the cinema, but instead has a completely different code?  And most importantly have you figured out what it's for?

At the very start of the game, there was a gate you had to deactivate in order to leave the courtyard.  The solution you have can be used on the same mechanism that opened it.

Darting between treehouses. Nice set of (star) puzzles. All done bar one which also has some squares inside a couple of grid squares, which I still don't understand (and opening theories haven't worked). A couple of the platforms turned a corner unhelpfully, meaning they don't join up. Hmmmmmm.