You dig through the rubble and create a new extension to your mine. You grab your sharp piece of stone, estimate your current depth and scribble '40' to the wall. Unimaginable depths. You have reached unimaginable depths. The earth around you shifts and moves, and the mine feels extremely unstable. You need to tread very lightly. The air is steaming hot and hard to breathe, and the noises around you are extremely disturbing.