Llandudno copper mine in the Great Orme @ 10min 40. Was it really less than 30 years ago that they were rediscovered?
https://www.bbc.co.uk/iplayer/episode/p00mlrqc/the-story-of-wales-1-the-makings-of-wales
In 1971 when I was working foir a Canafian mining company my wife and I looked over the Great Orme and could find no access, although one deep vegetation choked adit outlet might have been pushed harder if it had been more important to us.
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