It's below the rocky bit.
Here's Dan's old approach description:
I usually park in Stanshope, and then follow the path into Hall Dale through a couple of fields. Once over the last wall, I turn left and go up the steep slope formed by the side of the valley, right to the top by the wall. Now follow the wall along (passing two gates) to where a short barbed wire fence leaves the wall, and goes diagonally towards you, down the hill. Walk between the end of this and a small rocky knoll, heading down the hill. The cave is pretty much directly beneath this knoll - just where the bushes and trees start.
