The obvious things should be covered (Viking ships, Vigelandanlegget/ Frognerparken) etc. I second the Opera House roof climb. Not possible at the War Memorial Opera House either, AFAIK! Very close to your hotel. If adventureous, it is possible to rent skis if there is snow on ground yet (there is now, but might change before you arrive). Much night life/ restaurants is in the Grünerlřkka area. If you want traditional Norwegian food, Kaffistova at Best Western Bondeheimen is the best, or you could eat lutefisk at any number of retaurants specialising in pre-christmas celebrations. The latter (fish prepared with caustic soda is very popular in Minnesota, and among some Norwegians, yours truly not among those...)