At the far left-hand side - the red line is the approximate quarry face line, and the greyed-over bits are parts that are no longer accessible, the thing to look for when finding the climb down in the quarry face breakdown is a p-hanger above the hole that leads into the system. There's also a second entrance not shown on the plan, that's just under the quarry face and if you go in there and turn left, that'll take you on some hands-and-knees crawls to the top of a short shaft with an old gym rope on it that leads to the coffin level into Crichman Chamber