Powell climbed up to one robot and Donovan got up on another. There were seats on the back of the robots, and two long ears to hold on to. The two huge robots moved through the door and along a narrow passage into the tunnel. They moved slowly, at a speed that never varied: they were unable to hurry.
After a time, they came to the end of the tunnel and they went up some stairs to a tiny substation, empty, airless. A tall cliff of black rock cut off the sunlight, and the deep night shadow of an airless world enclosed them. Before them, the shadow of the cliff reached out and ended suddenly in a hard