Vienna has always been a city of grand contradictions—imperial and intellectual, ornate and avant-garde, deeply rooted in tradition yet perpetually restless. As the seat of the Habsburg Empire for more than six centuries, it was one of the great cosmopolitan capitals of Europe, drawing artists, composers, architects and diplomats from across the continent and beyond. That international character endures: today Vienna is one of only four cities in the world to host a United Nations headquarters—a...