So Frost Grave is supposed to be an Urban(ish) environment but to me the game sort of screams "dungeon" as in Dungeons and Dragons. I wanted to have a least some sense of this on the board so.AJ's templates painted it black added some rocks to indicate the entrance. I was going to do rocks all around but realized that would make the piece quite heave so used cork pained gray to resemble stone instead. Its not perfect but it does define it as a set off area.
With my stalactites and fungus(with some scorpions to make it scary) from Reaper added in we have something that seems cave like.