Well to be honest, most of the mountain biking in this area is pretty advanced - although its amazing, its generally steep and technical.
If you looking at more fun / relaxing things to do:
-Kootenay Lake, huge lake with awesome views, loads of beaches, fishing etc.
-Lakeside park in Nelson has a nice beach (on Kootenay Lake), kayaks & sups for rentals, lots of grass, shady trees. Half the town is chilling down there when its hot
-Kokanee Creek Provincial Park, about 25 mins north of Nelson, also on the lake with nice beaches, nice car-camping sites. Also close to Kokanee Glacier Park which is a mainly back-country park with lots of good hiking. You can camp there as well (there's even a 'hut' up there which you can reserve in summer that is used for skiing snowboarding in the winter)
-Ainsworth Hot Springs, another 20 mins north from the park, natural hot-springs fed into a pool with a cave etc. Nice way to relax
-Slocan Lake / Valhalla Provincial Park, a little further but awesome beaches and hiking in the park. There's whitewater rafting on the Slocan river too
That's barely scratching the surface, but 2 days doesn't give you much time. Feel free to ask any other questions or shoot me a PM