My last hotel stay in Oslo was a few years ago but Best Western and possibly other chains have a European Senior rate. It used to be good for all AARP members but I think they now have an age limit of 60. I've been staying with friends in recent visits so I haven't tested this out lately. What I used to do is check the BW site, check the consolidators -- do a lot of comparison shopping. Thon hotels have some reasonable properties and their predecessor (Rainbow hotels) had a senior rate.

Before turning up your nose at Best Western you should know that BW has some nice European properties with charm. A few years ago I stayed in a lovely new boutique BW near the waterfront, but it's since been bought by another chain. The franchises seem to shift around a bit from year to year.