By all accounts copper has been mined here since the Bronze Age 4,000 years ago, but production was seriously stepped up and exploited by the Romans.  The entrance to the mine is high on the hill and the opening is impressive, leading to passages which go on for miles.

My having read about other visits Charlie has made over the years, leads me to think that they could be a tad dangerous in these days of Health and Safety rules.  Which is why you can only access them under the guidance of a recognised caving club.