They drowsed as the sky on the eastern skyline turned a deep purply blue. Coyote hummed a little tune to himself, sounding as if he had eaten a tab of omegendorph, as he often did in the evenings at Zygote. Gradually it became clear that the skysill was very far away, and also very high; Nirgal had never seen land so far away, and it seemed to curve around them as well, a black curving wall that lay an immense distance off, over a black rocky plain. “Hey, Coyote!” he exclaimed. “What is this?”

“Ha!” Coyote said, sounding deeply satisfied.

The sky lightened and the sun suddenly cracked the upper edge of the distant wall, blasting Nirgal’s vision for a while. But as the sun rose the shadows on the huge semicircular cliff gave way in wedges of light that revealed sharp ragged embayments, scalloping the larger curve of the wall, which was so big that Nirgal simply gasped, his nose pressed right against the windshield— it was almost frightening, it was so big! “Coyote, what is it?”

Coyote let out one of his alarming laughs, the animal cackle filling the car. “So you see it isn’t such a small world after all, eh, boy? This is the floor of Promethei Basin. It’s an impact basin, one of the biggest on Mars, almost as big as Argyre, but it hit down here near the South Pole, so about half of its rim has since been buried under the polar cap and the layered terrain. The other half is this curved escarpment here.” He waved a hand expansively. “Kind of like a super-big caldera, but only half there, so you can drive right into it. This little rise is the best place I know for seeing it.” He called up a map of the region, and pointed. “We’re on the apron of this little crater here, Vt, and looking northwest. The cliff is Promethei Rupes, there. It’s about a kilometer high. Of course the Echus cliff is three kilometers high, and the Olympus Mons cliff is six kilometers high, do you hear that Mister Small Planet? But this baby will have to do for this morning.”

The sun rose higher, illuminating the great curve of the cliff from above. It was deeply cut by ravines and smaller craters. “Prometheus Sanctuary is in the side of that big indentation there,” Coyote said, and pointed to the left side of the curve. “Crater Wj.”

As they waited through the long day Nirgal looked at the gigantic cliff almost continuously, and each time it looked different, as the shadows shortened and shifted, revealing new features and obscuring others. It would have taken years of looking to see it all, and he found he could not overcome the feeling that the wall was unnaturally or even impossibly huge. Coyote was right— the tight horizons had fooled him— he had not imagined the world could be so big.