Great route, with lots of tourist-sights along the way (such as Heddal church, one of very few Stav-churches).
KONGSBERG take rv40 northover for 5km. then turn left onto rv37 follow this for 40km. turn south onto rv361. ( ignore signpost to Rjukan ) after 10km turn right onto E134 follow this for 4km. then turn right to TUDDAL og GAUSTADTOPPEN the road climbs steadily up to 4000ft. and then drops steeply down into RJUKAN. There are fine views of Gaustadtoppen ( 6000ft.) and a nice view on the way down into Rjukan. It is worth visiting Vemork the factory that made Heavy water during the 2nd world war, and made famous by the film Heroes of Telemark.