The Last Castle
According to Foreverness Vance wrote the story in Tahiti. (ref)
Nebula Award for Best Novella.
Hugo Award for Best Novelette
Castle Hagedorn occupied the crest of a black diorite crag overlooking a wide valley to the south. Larger, more majestic than Janeil, Hagedorn was protected by walls a mile in circumference and three hundred feet tall. The parapets stood a full nine hundred feet above the valley, with towers, turrets and observation eyries rising even higher. Two sides of the crag, at east and west, dropped sheer to the valley. The north and south slopes, a trifle less steep, were terraced and planted with vines, artichokes, pears and pomegranates. An avenue rising from the valley circled the crag and passed through a portal into the central plaza. Opposite stood the great Rotunda, with at either side the tall Houses of the twenty-eight families.
Republished The Last Castle, Spatterlight 2012.