Not a cave or mine, but most definitely underground (at 18 mins):
https://www.bbc.co.uk/iplayer/episode/b0bsrqfw/pubs-ponds-and-power-the-story-of-the-village-series-1-north-east
Thanks for sharing. Such a fascinating location. The fact that you can only get there by being rowed across the river adds to the enjoyment of a visit!
