How do I get to the lower level of the Wretch Warrens? In the hintbook, the trapdoor location is shown as "D" in the southwest but there's nothing there but a patch of cactus. There is a trapdoor a bit north of "D" but it leads underground to a storage area with a locked gate (with a lock that can't be picked) on one end. Are there 2 trapdoors in the Wretch Warrens and am I missing one of them? Or is there only one and I am just not able to find the right key for it?