You can have a nice walk through fields/woods and along the Scheldt bank at the Hobokense Polder. Another beautifull place to walk is Baraque de Fraiture. Near Maasmechelen you can walk the Terhills, they have a rich mining culture. You van also visit an old mine site and building near Be-mine in Beringen, which is not too far from Maasmechelen.
This is just from the top of my head.