Trip from Interlaken to Brussels

Strasbourg and Colmar are both nice places to stay overnight. Both have some pretty half-timbered riverside buildings, although Strasbourg is a much bigger city and areas at the edge of the centre are a little "gritty".

I've never been to Dijon, but whether you pick it would depend on your train route. Dijon is on the modern fast train route using TGVs, while Colmar and Strasbourg are on the traditional express route between Switzerland and Belgium via Luxembourg, which still has a couple of trains a day. It's now slower, but there is some very nice scenery, especially in northern Luxembourg and southern Belgium.

The logical route from Interlaken to Brussels is due north, via Basel (a Very Nice Place) and both Colmar and Strasbourg (both Very Nice Places) are just north of Basel.

Dijon (which others than me like quite a lot), and nearby Beaune (which I and others like quite a lot but Ed doesn't) is, to my mind, out of the way, but is available on TGVs, and then an expensive change and train to Brussels.

"The logical route from Interlaken to Brussels is due north, via Basel .... Colmar .... Strasbourg"
But, the quickest route is TGV Basel to Paris Gare de Lyon, Métro to Gare du Nord and then TGV to Brussels.
But if you want an overnight stay "quickest" is not important.
Yes to Colmar, Strasbourg or Dijon. Other possibilities Luxembourg, Lille or even Paris itself. I liked Trier (50 minute detour from Luxembourg).

From Basel to Brussels via the "Traditional route" there is one through train per day, otherwise you need to change twice, Strasbourg and either Nancy or Metz.

Thank You everyone for your answers. I am going to research all of them. I'll post again after researching

Colmar and Trier sound awesome! Which breaks up the trip nicely! We had planned to stay in Brussels because it was so centrally located. Would Bruges or Ghent be a better choice? I thought by staying in Brussels we could do a day trip to Paris, Cologne, Ghent, Bruges and Antwerp. We will be flying out of Amsterdam so our last 2 days will be in Amsterdam. Thanks