Yeah, Chris and I had a stamp round there after a trip to Cliff Rigg. Probably last year I think.
Only the quickest of looks as it was getting dark and didn't find anything of note though that's not to say there isn't anything there. Certainly shouldn't be any underground access of any particular size.
Certainly looks nothing like that now.
There's some more pictures in Richard Pepper's Ayton book which I think you have?