Finlandia Hall (or Finlandiatalo) is Helsinki's concert and congress hall. It is also an architecture masterpiece by famous Finnish architect Alvar Aalto (1898 - 1976) who was sometimes referred to as the Father of Modernism. In Helsinki, Aalto wanted to realize the major plan for a grand square and avenue flanked by cultural buildings, including the Parliament Building, first thought of by Eliel Saarinen in 1917 when Finland became independent of Russia. He drew plans for a grand center to Helsinki in 1961 and modified them in 1964 and 1971; you could say the city was a lifelong project of his.
Finlandia Hall was designed in 1962 and built between 1967 and 1972. The congress wing followed in 1973 - 75. For Aalto it was a major part of realizing his grand plan. The building shows many of his ongoing concerns - few right angles, design around existing trees on the site, the use of Italian marble and Finnish granite. The building is worth visiting but you can only do so on a guided tour, held on irregular days in the afternoons - check the website for dates.
It's a great tour. Specially if you don't have much time in Helsinki. :)
Trams 4, 7 and 10 go to Finlandia Hall, get off at the stop for the National Museum.