It is pitch black. You are likely to be eaten by a
The grue is a sinister, lurking presence in the dark places of the earth. Its favorite diet is
adventurers, but its insatiable appetite is tempered by its fear of light. No grue has ever been seen
by the light of day, and few have survived its fearsome jaws to tell the tale.
Mining in a certain area turns all exposed skin (maybe just parts that are actively disturbing the chemicals that cause the reaction) of the those doing the mining to a dark blue color. Will wear off taking as many years/days spent in the mine.