Introduction to the old pit of the open-pit mine: The old pit of the open-pit mine is the largest man-made sinkhole in China. It is a magical creation that combines nature and artificiality. It is more than 1,200 meters long from east to west, more than 600 meters wide from north to south, and has a vertical depth of 180 meters. rice. Looking down from the air, it looks like it was pressed out by a human thumb.