You need perception 15 or more to find the mining room/crawler nest area. It's in the second tunnel (uphill cave) in the most bottom right place of the cave. (first one being that one where you can build a camp.) If you're under perception 15 it says that it is a dead end.
You have two spots inside the cave crawler nest area, they are both near each other in the bottom right part of the area, both being marked by a question mark.
You can increase your perception from drinking Focus Tea or by equip items/armor that increases that stat. (You can increase it while leveling up, but I personally wouldn't grind for that long.)