Hideous monster? That thing was what happened to a person who had climbed in the hole....MONTHS later.
Perhaps it's reassuring that there's an end to the tunnel (now what happens when they actually reach it...can their bodies still support themselves?), but in no way is it reassuring that the story is guaranteeing that the people who went into their holes (which the story suggested that everyone who knew about theirs would) not only would be trapped in complete darkness surrounded by stone only able to very slowly move forward for months, but that they WOULD NOT DIE FROM THIS.