The Rue D’Aerschot, which you can see when arriving at Gare du Nord by train, is the centrum of Brussels’ Red Light District. The girls here are mostly Eastern European and seem to enjoy playing Candy Crush on their phone all day. If you’re into something more exotic or saggy, you should explore the blocks (more specific the Rue de la Prairie, Rue des Plantes and Rue Linné) around this strip since this is where the old and/or African hookers are located.
In comparison to the windows at the Rue D’Aerschot, these brothels look quite crappy. According to Reddit user GentleAnusDestroyer, prices are around €40 for a standard suck and fuck. If you want extras like more time, anal or ballbusting, you have to pay extra. BTW: make sure not to flaunt your money and gold jewels here because these streets can be quite dodgy at night… It is forbidden to take pictures here (both the police and ladies don’t like it) so please keep that in mind.