Troldhaugen - you could visit the home of composer Edvard Grieg. We were there in 1995 and took one of those guided tours. Don't know if they changed them over the years, but I found it interesting. Guided tours of the villa run continuously.
Entrance to exhibition, villa and garden:
Adults: NOK 50 (6,6 €)
Students: NOK 20 (2,64 €)
In the Festplassen, in front of the Rikstelefon, there is a statue of Grieg, the father of the classical music in Norway.