Belgium has a long love story with comic strips. A lot of authors and cartoonists were born there. As a result, Brussels has decided to honour this heritage with splendid murals scattered through the city.
The tourism information centre sells maps for a small fee with all the locations of the murals.
Bonom is a well known French street artist. You can find his art in all the city. He paints at night, hanging from a rope. Some of his art is even legal. For example, the Natural History Museum asked him to represent skeletons of dinosaurs at its entrance. After issues with the police, his identity was unveiled and Vincent Glowinski now has his very own website: http://www.vincentglowinski.com
Allée du Kaai
It is right in front of Tour & Taxis, one of Brussels landmarks. In summer, you can take a regular waterbus or a boat tour nearby. Have a drink in Tour & Taxis and then head back to the Quai des Péniches for the Fresque Kosmopolite Art Tour. You can finish your day by resting at Bruxelles-les-Bains, the local summer "beach".
If you continue your walk along the canal up to the MiMa, you will see some nice pieces of art on the surrounding walls.
The Giants of Anderlecht
Giant paintings on the pillars of the Neerpede. You could spend hours there. Do not miss the nearby parks and the centre of Anderlecht is also worth a look.
Bruxelles Chapelle Train Station
The whole area is full of street art. Stroll around and you will not be disappointed.
Quartier des Brigittines
De Wand tram stop
This is the largest mural in Belgium, near the atomium and the amazing Chinese Pavilion and Japanese Tower. Not far, you can also visit the beautiful Cathedral of Laeken.
There is of course much more street art to be seen in Brussels, including erotic art, as an unknown street artist is currently decorating Brussels with graphic images. Brussels policy in this matter is that is is up to the owner to erase or keep the paintings on his walls.
Bonus - Delhaize Molière
I haven't been yet but this former supermarket is becoming a huge street art hub.