The Enquiries of Doctor Eszterhazy (original 1975; edition 1975)

Avram Davidson was like no other writer, ever. He was deeply erudite and fascinated by weirdness. Nothing in the world was ever weirder that the Dual Monarchy of Austria-Hungary, about which Davidson wrote these stories.

This tour-de-force set in the Kingdom of Scythia-Pannonia-Transbalkania, "the fourth-largest empire in Europe," is not like any other alternate-universe fiction you've read. Davidson was one of the best writers ever to grace the sf/fantasy field, and it's a crime that his work is so hard to find.