21er Haus This building was constructed in 1958 as a temporary exhibition space for the Brussels World Expo. The Austrian architect was Karl Schwanzer (1918–1975), who had won the national competition for this project, beating entries by Oswald Haerdtl, Otto Niedermoser, and Erich Bolternstern, among others. He later wrote in his book Architektur aus Leidenschaft: “... maximum effect should be achieved with minimum effort.”