Oh I agree that there should have been more info about it before it was done. It's a pretty big thing to chuck in, especially as originally it seemed to be all about returning it to it's original condition, but yeah I guess monitoring it is a requirement if the voids are that big. My only point is that if the trench is in the floor of the current tunnel, then it's mostly in natural material, not original Neolithic building material, because the current tunnel floor is beneath the original Neolithic ground surface which the hill is built on top of. I think..