Hodge Close: the hole I was looking out of is top left-of-centre here (you can just make out the rusty rails above the water):
You get there either by fixing a rope and abseiling down the quarry wall, or by walking a couple of hundred yards north and descending into the neighbouring quarry, Parrock, on an easy path then along the quarry bottom to the mouth of the 'ole. Guess which one I did
Cathedral Cavern's even easier. A quick pint in the Three Shires Inn, then over Slaters Bridge, turn left and right, and climb *up* to the entrance, you can't miss it...