That's a lovely atmosphere you got!
As for the "empty" corner, I does not bother me much, but one way to deal with it would be a vignette. I would also crop the lower part of the image, at least halfway between the rock and the image bottom... that would bring the horizon, currently smack in the middle, closer to the lower third. Alternatively, there is one format that goes well with symmetrical composition, and that is a square one.