This is a nice run in Provinciedomein Kessel-Lo, Leuven’s largest park. It can  be combined with canal paths extending north in the Vaartdijk suburb.

Path along the canal. Google Street View

The park itself has 4-5 km of scenic paths, around fields and a couple of small lakes. There’s also a swimming pool and recreational facilities.

For a longer run, we recommend the paths along the Leuven-Dyle, extending north. We’ve mapped a route from the north end of the park to the canal path. For a long run, we recommend crossing to the west bank in Keierveld. It’s possible to run for many km along the canal, with paths on both sides (though few places to cross).