"What is mauritanium?" Ax muses as he steps through the door and heads north. He moves strangely, as if laser-guided; in fact, he is, since he has a nearly eidetic memory and an excellent sense of direction.

After a few minutes' walking, a tunnel mouth yawns ahead, wide enough to accommodate three adult humans at a time. It descends nearly vertically to the horizontal tunnel below. The walls of the tunnel are slimy and exude a foul smell.

"I have not yet installed a tunnel at this entrance. It is freshly dug, and therefore slippery," Ax apologizes. "The smell and the slipperiness will abate with time. I can go down first and assist you if you believe that will be safer."