If you plan it right and visit Place Sablon first, you can walk to Square Brueghel L’Ancien in the Marolles area and take the outdoor glass elevator up to Place Poelaert (for free).
When you reach the top you will see the fantastic panoramic view of Brussels with three major landmarks in the distance on a clear day: the Basilica is just of center, the tip of Hotel de Ville and the Atomium to the right.
The center piece of Place Poeleart is the Infantry Memorial of Brussels, which stands in memory of the Belgian foot soldiers who fought in World War I and II. It stands between the Anglo-Belgian War Memorial (commemorating the support given by the Belgian People to British Prisoners of War during WWI), and the Palais de Justice de Bruxelles.
Place Poelaert, is home of the Palais de Justice, Belgium’s supreme court. Designed by architect Joseph Poelaert, the building three times the size of the Royal Palace and commissioned by King Leopold II, it was finished in 1883 after 20 years of construction. It unfortunately has been under construction for a few years and the scaffolds don’t do the building justice as it obscures its beautiful architecture and size.
Place Poeleart is definitely worth the stop, you may even find yourself gazing at the city and losing track of time, especially if visiting at sunset.