Scenic route from Brussels to Luxembourg City?

Waterloo and Namur with its cliff-top bastion.

But mostly just grin and get on with it, watching carefully the drivers around you. Belgians (white number plates) - generally poor drivers, ignore what the turn indicator says (this car comes with a turn indicator?? Is that what this stick does? What does it mean??? Do I indicate right for a left turn or is it the other way around), expect them to cut you off after passing, expect trucks to pull out in front, expect their speed control to be "imaginative", or to suddenly brake for no reason.

Expect Luxembourg drivers (yellow number plates with short numbers on usually large cars like Land Rovers, huge Audis) to drive like Belgians at the speed of Ferraris in Germany regardless of the 120 kph speed in Belgium.

There is a nice IKEA on the Belgian side (just) of the border.

Run your fuel down to nearly empty before reaching Luxembourg. All filling stations in Luxembourg are the same price, varying by no more than 2 or 3 tenths of a Euro-cent per litre. Even the motorway services are the same price - government controlled. Yay Luxembourg government!

It really isn't a scenic route, and I don't know of one. It will get you to your destination.

This is driving in Wallonia, like a different country from Flanders. My observations are based on 20 years of driving in Belgium.

If you don't absolutely have to drive there are direct hourly trains from city centre to city centre Brussels/Luxembourg.

Oh, I forgot to add - roadworks. Lots of roadworks. Watch your speed in roadworks - radar will be watching too.

The route thru Dinant is lovely. Plenty of sites--castles--along the river valley. Dramatic scenery.

A bit off the track to the west, the Orval Abbey site is lovely.

Have not enough experience to recommend wholeheartedly a scenic route through the Wallonia part of Belgium, but the northern part of Luxembourg country is certainly worth driving through with cute places like Vianden, Echternach and Esch-sur-Sûre. You can drive from Brussels via Liège (but skip this place) through the countryside to Luxembourg. Little Durbuy and way more east Monschau (very touristy but nice) just across the German border can be worth a visit.

Edit: A visit to Orval Abbey is well to combine with Bouillon, the medieval castle there is worth a visit.