One of the nicest ways to discover a city is to look at it from a high point. Many cities have hills or skyscrapers with roof terraces… Brussels has Parking 58!
Parking 58 is situated in the very center of the town, 600m from La Grand Place (the main square, a Unesco Heritage site!!). When you enter, take the lift on the right and go to the 10th floor. A big parking terrace will open right before your eyes. From there, you have a beautiful 360 degree view of Brussels.
My suggestion is to go there as soon as you arrive in town: check out the highlights from above before getting into the crowds. And then, just before leaving the city, pop up there again and recognize all the places you’ve discovered during your stay. It will have a different meaning for you.