User blog comment:IamJakuhoRaikoben/Chapter 372: Breach, Review./@comment-4449950-20140312110503/@comment-7418318-20140312132813

In my opinion a cave is quite different from a valley.

With there being pictures that show Face beneath a sky, I think we can rule cave and cavern out simply because of the context, even if by the words alone it's a possibly correct translation.