Reading the comments on here and I see there's a letter in the cave? How can I find it?
You can find it after You build the stables and get the horse from the merchant I think
First you need a source of light, so you must complete a quest (there are two options, one is in the lizard's temple and the other is from the witch) whatever you chose, will give you something to equip yourself and then you can go to the cave 😉