I'm at the same place Lorenzo is, I guess.
Spoiler
I've found all three caves. Took me a while to understand that the object on the beach wasn't a cave! I guess the hidden message is a hint to where I can find an object to help me past the obstacle in the third cave, and I further guess this must be somewhere in the large cave. This game is super hard, but the objectives helped. Not given up finding the second ending yet!
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