I came so close to going down one in my teens, slipped in some dry casuarina needles when I got too close to a hard rock shaft while out bowhunting any pigs I could ambush or really brazen foxes I could call that were feeding during the day. I had put my bow down beside a tree to have a closer look at the shaft, the bow slipped and almost went in but as I lunged for it I too slipped in those darn dry pine needles, was quick enough to grab hold of some exposed roots and then slip my foot over the bow as it was going over the edge.
Discovered there was an adit about 150m down and across from it with drifts and further vertical shafts branching off past the one I near went down, there was no evidence of an old headframe so might have just been a ventilation shaft, not sure, there were quite a few sleepers at the bottom of the shaft so maybe they were the headframe tossed back in.
I still think about how close I was to lights out.....possibly 30m down jagged rock sides to a pile of sleepers that went god knows how far down below the now waterline of a cross section in the tunnel. I'd still be there King of the Jenga pile, grinning at any hapless bugger that stumbled across the old mine, although pretty fair chance of no one being back there since I came across it.