“If they veered left, it would feel to them as if they were sinking into the earth: the path would narrow as the ground around them rose up to their hips, then shoulders, then heads. The walls would turn from sod to stone, and it would seem as if they were walking inside a crag in a cliff. The sky would be reduced to a thin swath of blue, broken in parts by the branches of the trees that grew above them along the sides of this ancient channel.”