The 21er Haus Museum of Contemporary Art was built in 1958 by the Austrian architect Karl Schwanzer (1918-1975) as
a pavilion or temporary showroom for the Universal Exhibition in Brussels. Schwanzer had won the Federal Governments
competition, in which he had prevailed over such competitors as Oswald Haerdtl, Otto Niedermoser, and Erich Boltenstern. Later,
he wrote in his book Architektur aus Leidenschaft: "... maximal effects were to be achieved with minimal efforts. Austria
could not afford to spend more than 35 million schillings for its pavilion for the 1958 Universal Exhibition - a tight budget
when compared to those of other participating countries. According to Schwanzer, the starting point of the concept was "the
humanist idea that makes man the centre and measure of cultural and intellectual progress". It was a contribution entirely
in line with the Expos motto "Striking a balance for a human world".
The architectural structure of the pavilion seemed to be floating. Taking into account the inferior quality of the plot at the Parc Royal, the building was conceived in the lightweight construction mode, with its upper storey, measuring 40 by 40 metres, resting exclusively on four buttresses. Robert Krapfenbauer, who later collaborated in the planning of the Vienna Donauturm, was responsible for the constructions statics. In 1958, Schwanzer received the Grand Prix dArchitecture for his visionary and technologically innovative design. Fritz Wotruba was commissioned with the monumental figural relief to be installed in front of the pavilion.
It was not least owing to the former Secretary of Education Heinrich Drimmel that the Austrian pavilion was eventually used in a permanent fashion as Museum of the Twentieth Century. On 30 January 1958, the daily newspaper Die Presse described the exhibition hall originally designed for the Expo as "a virtually ideal foundation for a Museum of Modern Art". Karl Schwanzer adapted the steel skeleton construction to the museums purposes: the ground floor was glazed, the courtyard was covered with a roof, all façades were substantially modified, and the whole structure was reinstalled in the Schweizer Garten. The new museum was opened on 20 September 1962. One of the comments about the institution and its first exhibition, Art from 1900 to the Present, said that the museum represented such a break with the Viennese museum tradition "that one automatically felt as if on foreign territory when first entering the museum". The art historian Werner Hofmann wrote on the occasion of its opening: "This new building bears the signature of our age, and its spatial layout does justice to the fact that the art of this century displays a powerful and frequently aggressive self-confidence that calls for vastness and openness."
The building served as an exhibition hall for the Museum of Modern Art until its collection was moved to the Museum of Modern Art - Ludwig Foundation in Viennas new MuseumsQuartier (the former Court Stables) in late 2001. The 21er Haus Museum of Contemporary Art was finally incorporated into the Belvedere in the early summer of 2002.