There's mention of the cave and a "convergence point". I tried looking all around the cave, but there doesn't seem to be anything there (although you can find the drawings on the walls)

Edit: I looked at the source though and I don't see anything else clickable in the cave... No hidden secret badge either, maybe it is just for ambiance.

Turning the antenna in the treehouse gives different messages of about two minutes each. It’s a bit hard to listen to the whole thing without someone else interrupting by changing the antenna, so here are the audio files:

https://neal.fun/cursor-camp/sounds/harold-1.mp3

https://neal.fun/cursor-camp/sounds/harold-2.mp3

There’s talk of the tent near the beach, the gong, and gathering at the big fire once you hear the call. There’s also talk of the cave, the star map, trusting the bats, and reading the right side of the book carefully. Though it seems to me the audio may be outdated and that the star map was initially in the book and was since moved to the telescope.

The right side of the book mentions the time 8:47.

If we look at the star map, only two of them are pointing inwards. If we consider that a “convergence point”, it should be around the area of the big fire and tent.

That’s as far as I’ve got with this.

There's also a locked door in one of the buildings, but I couldn't figure out what either mean if anything. It would be cool if the radio was used for something though

The radio in the treehouse might be relevant. See my sibling comment.

https://news.ycombinator.com/item?id=47961275

Yeah I saw that too, but the list of all accessible rooms is also in the code and the only scenes I see are

  default
  sauna
  tent
  cave
  treehouse
  house-main
  house-cafeteria
  house-bedroom
  house-trophey
  boat
  telescope
It would be really cool if there were some secrets, but alas it appears not (unless it's obfuscated in the source as well)