Originally posted by FissionChips:

Did anyone seriously go up those stairs and not break out that wooden wall? You've also got windows at ground level indicating something is in there. I don't think this is a secret.

I didn't see it first time. The whole thing was buried into enough mountain that it wasn't clear there was something there, and add to it, I missed the wood panel, saw the stairs and walked right on up them without really looking side to side.

search carefully, there is a unique item down there, or most of the time seems to be at least 1 copy...