the barony
Rosendal is famous for having Norways only Barony (http://www.baroniet.no/en...). The small castle, wich dates back to 1665 is surrounded by a beautiful renaissance garden.
During the summer seaon the Barony frequently have events like concerts, theater plays, art displays, and of course guided tours around the castle and the surrounding gardens.
Note that the english version of their homepage is somewhat incomplete.
the shipbuilding museum
Located just by the harbour, the Shipbuilding museum is open during the summer season.
kvinnherad church
The Kvinnherad Church, is a medieval church built of stone in 1250. The church contains both artwork and the Rosenkrantz burial chamber with some beautifil sarcofagus.
The church is open for guided tours during the summer season. More info on the Barony website.