Grand Place is the central part of the city where no vehicles are permitted. You can walk up to the Grand Place and get in the awe of its architecture. The city hall & other guild halls in the center are beautiful. During important days, there are special light & sound shows on the structures & according to the theme of the festival, you will also find decorations, stalls & many more things in the Grand Place.
Grand Place is definitely one of the best things to do in Brussels, especially during festivals.