She took the title role of "Turandot", which is brief but requires an unusually big sound, to La Scala in Milan in 1958, and then to the rest of Italy. Nilsson made her American debut as Brünnhilde in Wagner's "Die Walküre" in 1956 with the San Francisco Opera. She attained international stardom after a performance as Isolde at the Metropolitan Opera in New York City in 1959, which made front-page news. She said that the single biggest event in her life was being asked to perform at the opening of the 180th season at La Scala as Turandot in 1958. She performed at many major opera houses in the world including Vienna, Berlin, the Royal Opera House at Covent Garden, Tokyo, Paris, Buenos Aires, Chicago, and Hamburg.