There's lots of lovely walks just a short drive form Aviemore, including those at Rothiemurchus.
Woodland walks are lovely at any time of year, but they are particularly pretty in the autumn as the leaves begin to turn. One of our favourites is the walk to the Lily Loch (Lochan Mor) from Rothiemurchus. It's about a 5km circular route on nicely maintained paths and tracks, or you can walk it as an out and back to the loch, retracing your steps back to the car park. If you want to make it longer you could add on the trails around Loch an Eilein too, but that does make it quite a bit longer, adding another 5km. As an added bonus, you can reward yourself with coffee and cake back at the Rothiemurchus Centre, or a bowl of one of my favourites - cullen skink,