If you want to get away from the coast and all the traffic down there, you should ride this route.
Passing mostly through farmlands, forests and hills it is very nice.
There are some places to stop for a rest (if you bring your own lunch and coffee)
or you could stop in charming Åmli-town or Treungen-town.
Both places have good restaurants/cafes.
Take the inner route to go from south to east in Norway! Compared to the coastal E-18 which have an overload of traffic cams, police, 60 km/h speed limits and huge loads of traffic, this route offers you a variety of mostly narrow, curvy roads with many really nice bends, mixed with some long wide stretches where you can really "empty" the bike, or calm down and enjoy the beautiful wood/mountain scenery without worrying about the road. The route mostly runs along a beautiful river and the crystal clear Lake Nissevann, many places carved into the rock. Start off by finding Kristiansand airport, Kjevik, and follow road 41 all the way, paying attention at a few crossings where the route take an unexpected left or right. Especially between Vrådal and Brunkeberg at the end of the route, the road is an extremely curvy serpentine road descending into the Kviteseid Valley, and then back up to Brunkeberg through "scratch curves" where you can lean over as far as you dare. This upper part also recently (2004) received a new blacktop surface. Sadly it can be a bumpy ride some places along the rest of the route as this is not a primary road. Still I always select this road when going south from the Oslo area to Southern Norway - it is a secret playground for those of us on two wheels that do not live where the really spectacular roads are in western Norway.