The 20th century was unkind to Vienna. The capital of the Habsburg empire until 1918, it was, by early 1989, a bleak and battered outpost within touching distance of the iron curtain. Now that the city has undeniably recaptured its glory of old (symbolically, its population grew to two million last year, its pre-first world war imperial population), it might seem counterintuitive to visit it for its modernist architecture. But this is a highly rewarding endeavour, especially if one wishes to avoid an overdose of Sachertorte (chocolate cake), horse-drawn carriages, flamboyant churches and palaces, and imperial tat. Viennese Modernism, or Die Wiener Moderne, began much earlier than its European counterparts. As early as 1895, the most prominent architect of the day, Otto Wagner, announced the end of historicist and romanticist architecture, which had dominated the previous decades – there was to be no more neoclassical, neo-baroque, neo-gothic or neo-Renaissance. Max Fabiani’s Urania Observatory. Photograph: edpics/Alamy Two years later, the Vienna Secession emerged. An Austrian version of art nouveau, one of its main proponents was Wagner …