Long Tor Grotto is a decent little mine in Matlock Bath, protected by a small lake of the most evil and disgusting black sewage-laden mud I have ever seen. It's a bit like the Wallows in Peak Cavern, but with cold black stinking lava instead of water. There was a dead rat floating on top of it on my only trip, and it smells of shit and diesel mostly, with hints of dirty laundry on top. Fishing waders are
just long enough to enable you to get through without touching this horror, and they took about ten minutes of scrubbing in the river afterwards before I could safely put them back in my friend's car.
Amusingly, in ye olden days, they had a lemonade factory/shop above it (Whittaker's) which also operated the mine as a small showcave, and when we were digging out the Longcliffe shaft, in Castleton, we found a completely intact bottle, with stopper, buried about 10m down in the rubble - which didn't even begin until 18m down, so how this bottle survived is beyond miraculous. Mrs. Whittaker was clearly capable of serious stuff.
Anyway, I digress, as always