As we walk through the tall grass, we are surrounded by sheep grazing lazily in the afternoon sun. A patch of Black Wood forest appears on the horizon. We scale a fence surrounding the tree line. Suddenly a gaping vertical-hole stares us in the face. To prevent it from swallowing man or beast, a solid steel grid protects the vertical shaft. A small trap door allows access. So small that I have to take my camera bag off and let it through separately. A steel ladder leaning at