Nothing like replying to a 4 year old thread...
I've recently uploaded a couple of photos of the "large chamber" mentioned by Dave. This chamber appears to run through into the "large openwork", though access is blocked by very deep water.
I lived nearby and explored the whole site with a friend when we were was in our teens about 30 years ago, then had another look last week and it doesn't seem to have changed much.
The "large openwork" is now fenced around the top to prevent flytipping (it's half filled with rubbish), but a short adit leads in from below. This ends on a platform needing a scamble down (safer with a rope) into the bottom of the chamber. I didn't go down this time, but have been before and explored a couple of short tunnels leading off.
Further up the valley, near the road, is what looks like an earlier tunnel with a low opening behind an elder tree. 30 years ago this could be accessed for 100m or so, wriggling on your stomach over rough stone waste. It was the dodgiest cave that we found and not one I'd want to enter again.
BTW, hello everyone. I've been enjoying reading the forum but this is my first post. Great site you have here!
"The true crimefighter always carries everything he needs in his utility belt, Robin"