In the 4th level of the campaign (Castle Rendro), the impenetrable rock that surrounds the level is incomplete, if you dig through this the game will freeze. Since there is another Keeper that could do this, I suggest you to modify the level (with Adikted, since the original Editor doesn't allow you to modify the external layer of blocks) and put rock all around (I left the gems, since they are unbreakable)...