Captain Ban, son of the Warden, is told by an oracle that he alone must fly to the island stronghold of those masters of time, the Cloud-People.
Your world is a slope and you roll down it all the time. Down and down until you wear out and die.

Variants

(1)
  1. “The Covenant” by Poul Anderson, Fantastic July 1960.
  2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . written by Poul Anderson