The Ardenne region is full of things to do if you plan on extending your visit.
The countryside leads itself to walking. There are a huge number of well mapped out walks. Visit any tourist information centre and they have maps showing walks in great detail including the best place to start, how to get to the start (if you don't have a car) plus other info about the walk.
Nearly every town and village I have visited in this area is lovely to look at. They are so well kept. Even the smallest village appears to be wonderfully maintained with nice communal areas in the centre and well maintained gardens. There is certainly a big sense of civic pride in the area.
Due to the hilly nature of the area there is some good canoeing to be had.
If you travel down to La Roche-en-Ardenne you can book yourself a trip in a canoe from a number of companies. It's pretty cheap and convenient. On our last visit we did a 10k trip where they drive you in a minibus up the river and leave you to paddle your way back to where you started. They also do a 25k trip on the same river.
There are similar arrangements from the Durbuy area and I am sure many other places. It's well worth a go. It's also interesting to compare how health and safety regs differ between countries. When we went canoeing we were dropped off, given a canoe, a couple of paddles and off we went. Life jackets and helmets were optional. I am sure the last time I canoed in the UK we had to wear life jackets, helmets and were given a safety / instruction briefing!!!
There are a number of caves to visit. My favourite being those near Hotton. The guide was fantastic and made it a very worthwhile visit.
Of course this area has a large number of military museums to visit. Large towns have one or more but you will also find some very interesting museums in much smaller places. One I particularly liked was in a place called La Gleize which is only a short drive west of Stavelot.
There is also a great family adventure place called Chlorophylle. There is a link in the 'Useful Links' section although the website leaves a lot to be desired! However the place is excellent fun for young and old. Its situated quite a distance from the circuit, more over towards La Roche-en-Ardenne and Durbuy.
There are many other things I could write about such as animal parks but the Belgian Tourist board is well set up. A quick Google is all that is really needed to find a lot of different things to do.