It was the arctic wall, Equestria's northern frontier, a natural border stretching across most of the continent's breadth. The Crystal Mountains marched in stark majesty, blue and gray and white, around the tiny silvery mote that labored eastward up a long narrow pass. Below ran a single railroad track, visible only where snowdrifts had blown away. To starboard reared the western extents of the southernmost range; to port stood the overlapping eastern end of the next rampart. High above a white sun shone in a hard cloudless sky. Somewhere ahead lay the destination of both the rail line and the airship following it.