One of the places I'd like to take friends to when they come visit me is Halles Saint-Géry. I like its architecture and the atmosphere. During the day it functions as a cafe and exhibition center. Every first Sunday of the month, there is also a vintage market going on in the hall. But I like to go there at night the most, the lightening is awesome.
You can find all kinds of cocktails and Belgium beers there.
The last time I went there was at my birthday and we had long island ice tea. It was so long ago since I had long island ice tea. I'm not sure if it's still a popular cocktail but I had a lot of nice memories with this cocktail back 7 or 8 years ago when I regularly went out in China.
I'd recommend you visit this place once you come to Belgium.