Complex sentence: Between 1979 and 1980, work was done to restore the building and to remove additions and alterations which were unsympathetic to the original design, and the buildings was adapted for use as a museum by the Catholic Church.
Split into simpler sentences: Between 1979 and 1980, work was undertaken to restore the building and remove the additions and alterations, which were unsympathetic to the original design. The buildings were then adapted for use as a museum by the Catholic Church.