(1) Having lived some years in Mons/Bergen, rollerbladers (fitness) used to meet on the little parking (there are several) of the Lotto Mons Expo on Wednesday evening and Sunday morning during the good season.
This is polish concrete, maybe 9 or 10 lines of cones. It's 100% public except when there is an event in the building.
(2) Streeters used to ride since decades on the esplanade of the Fortis bank (avenue Frère Orban), there it's polished blue stone of Soignies, it's near the city center of Mons/Bergen. The bank employees allow skaters to come since they are used to (since the first skate board wave of the late 80ies). Maybe three lines there. It's cool because there are skaters, agressive inline skaters, and sometimes also BMXers. The surface is very smooth, agressive skaters shuffle on an easy way on it.
In Namur, from what I heard form Xavier M. (a rider from there):
(1) when it rains or during the winter they used to go in the gallerie Saint-Joseph (in front of the Eldorado) the Wednesday after 8pm
(2) when it's sunny, at the marina of Jambes (suburb of Namur, in front of the Casino).
Hope it helped
