Go to the Atomium! It's in a nice area and you can get a Metro from Brussel Zuid (get a day ticket for public transport) to Heysel. It's been done up, looks stunning, and if you like science the exhibitions inside are fascinating.
If you want a nice meal in the tourist area, there is the cheap kebebby option of Kaasmarkt just to the west of the Grand Place, otherwise known as Pita Street. On the other hand, the only restaurant within about a kilometre that my Brussels native friend recommends - and I've been there about ten times, always good, is t'Kelderke, actually on the south side of the Grand Place itself.
if you want to find out about the history, the open-top buses are very informative, if a bit expensive, but of course they offer the get-off, get-on later options, and they pass the Atomium.
Sorry if I'm over-enthusiastic, but in the light of what recently happened, I am delighted that you are going to visit Brussels in one of the, to some extent, most unjustly underrated tourist countries.