Since 1998 Brussels has held a monthly Critical Mass every last Friday of the month, at 18h00.
There are two starting points: one at Porte de Namur/Naamsepoort and another one at ULB campus Plaine parking 2. Both are marked on the map below. Every last Friday of the month at 18h. Both groups join up at the begining of the ride.
Other resources Edit
The "official" website is that of placeovelo, a collective not organizing the Critical Mass, but giving a lot of the input: PlaceOvelo/Critical Mass Brussels website