When was where the two legs of 1933 Mitropa Cup was played built ?
1933 Mitropa Cup:  The two legs were played on 3 September in San Siro stadium and 8 September in Prater Stadium. Ernst-Happel-Stadion:  It was built between 1929 and 1931 for the second Workers' Olympiad to the design of German architect Otto Ernst Schweizer.
between 1929 and 1931