While there's no ferry from Stockholm to the capital of Norway, Oslo is just a short plane ride away!
If you have the time (and the money) try one of the many helicopter tours offered in the city or go to one of Norway's many fjords and small villages in the surrounding area. But if you only want a quick stop, Oslo itself still offers plenty of things to see and do. Amongst other things Oslo offers a great collection of Viking age items and ships. A must do is also to visit the city's unique Opera House!