I'm not in remission but I flare badly over the Winter months and am generally much better over the Summer months. My stamina and fitness declines sharply every single Winter (and I gain loads of weight) then I work hard to get my fitness back up and weight down before I flare again. It is of course extremely frustrating to be stuck in this perpetual loop but I think it's important to try not to lose too much ground over the long term for as long as I can.
Basically in about April when I start to finally come out of my flare I can only walk a very short way so I spend a month to six weeks methodically going for walks in the forest I live on the edge of. These start at at a very slow speed and sort distance, and I systematically increase this until I back to 'normal walking'. Then I start walking faster and further and my levels start to come right up. Eventually the joggers and squaddies all smile and wave and then I know I have entered the realm marked as 'doing something a normal person might consider exercise'
Then I get the pushbike out and repeat the whole process on the bike. It is exhausting but worth it (at least so I tell myself)
I also do salsa based exercise when I can which is great fun and you can tweak quite well round your joint issues.
Ideally I like to swim regularly more that anything else (I find it the form of exercise which is least jarring and shows results fastest) but I find it hard to get to the nearest pool very often. Swimming is a good option if viable though in my opinion.
Like Angie, I tried the gym but I struggled with gripping the equipment and things. It's also just not worth my getting membership because I can only use it half the year.