A mirror and an encyclopedia lead the narrator to discover Uqbar, a country that exists only in one edition of one encyclopedia, which describes a world called Tlön where idealism is not philosophy but fact. Borges published this in 1940, and it remains one of his most unsettling stories. The imaginary world begins to infiltrate the real one; objects from Tlön appear; the encyclopedia grows. The story is about how ideas shape reality, about how fictions become true. The calm scholarly tone makes the impossible seem inevitable. We are still finding artifacts from Tlön. We always will be.