Thanks, and that is good question. For me it was a very special time, and Liege was far better than Mons, Ostend, Ghent and Bruxelles. It was much safer, unlike the Gare du Nord area, and there was a real variety of girls. Some local, others from NL - and not many from EE at the time (2004/5) when I lived there full time. I have had some equally good sex elsewhere, but in terms of ambience it was perfect for me. Rue Champion and Rue Agneau. Ghent and Aachen are the closest I have found to date.
I would park on the island of Outre Meuse - cross the bridge, and you get the first glimpse of the neon lights in the windows. I would then take a walk around the three little streets, before having a coffee - and then, show time. I had two regulars, and even though it was the standard 'window' type experience, it had some quite intimate moments as well.
The RLD was closed in 2015, and the other street of windows on Rue Varin, by the main station, is now under threat. This was always the more expensive option - with some serious porn star type girls. The price was double or treble. About 60 euro compared to 25 euro in the Rue Champion. The City have now increased the bar/hostess tax from 5,000 euro to 15,000 euro in order to close them down. Tragic.
And strangely enough the local press are complaining about the rise of street prostitution??? WTF, as the younger generation say...