Osztrák Postatakarékpénztár (Österreichische Postsparkasse)

This building, set just back from the Ringstrasse boulevard, is Otto Wagner’s masterpiece and one of the most important pieces of architecture of the modernist age. One sixth of global aluminum production at the time is believed to have been used in its construction – a milestone in modern architecture. Wagner also designed the entire interior: rugs, furniture, wall paneling and countless other details.