The Left Hand of Darkness (1969)

On Gethen, bodily sex changes through a cycle that the visiting envoy initially struggles to understand. Le Guin makes his assumptions part of the obstacle to trust, then brings dependence into sharp focus during a journey across the ice. This is an important variation in the selection: the changing bodies are ordinary biology within the imagined culture, rather than technological upgrades. Read for an outsider learning that his own categories are not universal. A standalone Ekumen novel.