The best way to start your visit in Brussels is by going to Place Poelaert. This place gives a good overview of Brussels. It is especially nice to visit during sunrise or sunset.
You can see all of Brussels buildings in a wonderful panorama. There are binoculars to view the buildings in detail and there is a lift that takes you to the Marolles. You can also walk down following the parking space of the adjacent Palais de Justice.
You can sit on the stone fence to admire the view. On your right there is a beautiful art deco building functioning as a high school and on the left there is the Palais de Justice. Right in front of Place Poelaert is Avenue Louise, following this avenue completely to the end, or taking a tram, will bring you to Bois de la Cambre, a large ‘park’ with a lake (see the Bois de la Cambre article).
The whole area is worthwhile to walk around in and to discover at your own pace and interests.