I'm posing in an old Lead Mine Entrance, in the title of a web site called 'Cave and Dive'. Actually they are often linked. More than one cave was entered by the miners in their quest for the precious ore, including the well known ' Lost Caverns of Grassington Moor'. These last natural caves can no longer be entered, because the shaft leading into them has since collapsed. Seriously folks don't try this at home.
Mines are very dangerous places, often more unstable than caves and much more liable to 'bad air'.
Not to mention the fact that most landowners are not keen on you digging large holes all over their land.