We enjoyed a one week June driving trip through the Norwegian fjords a few years ago. Since you have 12 days instead of 7, perhaps you could use our itinerary and add on to it....We flew into Bergen, picked up our car at the airport and drove to Voss (Fleischer's Hotel) for two days. On our full day there, we explored the area south-east of Voss. Day three we drove to Flam (very scenic road trip) and took the train up the mountain round trip, then stopped at the Vik Stave church before catching the ferry to Balestrand (Kvikne's hotel, OLD part) for two nights. Day five we drove past glaciers to Geiranger (Grand Fjord Hotel) for two nights. On our full day in Geiranger, we took the ferry round trip through the Geiranger fjord and part of the next fjord north. After that, we headed back to Bergen for a long afternoon and flew to London the next day. Since you have more time, you could continue north from Geiranger, then take an inland route back to Oslo. Driving in Norway is very easy - frequent ferries cross the fjords, tunnels go through the mountains instead of roads crossing the top.....Visiting Norway is a bit more expensive then visiting other sites in Europe, but it's worth every penny to see scenery which actually rivals Banff and Jasper.