Gruvfrun - Lady of the mine
There are many stories about Gruvfrun/Bergsfrun (Lady of the mine/mountain) in Sweden. She is often described as a beautiful woman. All mines had their own Gruvfru/Bergsfru. If you swore, whistled or acted foolish she could get angry and that could be very dangerous. If she appeared in black clothes, it meant someone of the miners were going to die.
But she could also send warnings. If you heard her knocking inside the mountain, you were blessed to be warned and should get out of there asap.