A Voyage to the Land of the Houyhnhnms by Jonathan Swift

A sailor journeys to a land ruled by intelligent, rational horses known as Houyhnhnms, where human-like creatures called Yahoos are regarded as savage beasts. As he spends more time in this society, he begins to admire its logic and peace while becoming increasingly disgusted by his own species. The story questions the nature of humanity, morality, and civilization. Through satire, it delivers a stark critique of human behavior. It’s the darkest and most philosophical leg of a broader journey.