I agree with Matt. There's a survey out there showing the thru trip. As per previous poster, I'm certain too that it was a Jules Barrett sketch.
Here's what I remember:-
The two entrances or entrance / exit are as described above. You shouldn't have any difficulty finding them in the Delph. Rig the grill entrance first if you want, but it should be free climb-able. If you are rigging it you'll have to retrace your steps a little way to the adit entrance. Walk / stoop along the passage from the adit entrance, mind the hole(s) in the floor and you'll come to a shaft with a large, sturdy pole across it. Drop the shaft. Swing off a short way down. Crawl and stoop a bit. Rig a small internal pitch as a pull through, follow your nose, climb down a small chimney (be careful at the bottom - it opens out). Follow your nose again. Arrive at the bottom of the grill shaft, climb or prussic out.
The route finding is simple enough, anything which doesn't get you to the inner pitch and the small chimney soon go blind. You can rig the main shaft as a pull through off a DCA ring on the main adit pitch or rig a Y if you are not confident of completing the trip. If you reach the pull through lower down, you are almost there and can't really go wrong. I did this about four years ago, so don't blame me if my memory is hazy.
Have fun, it's muddy down there.