Having dated a girl from Brussels for a few years, on trips over there, her brother would take me out to many different cafes which served specialitst Belgian beers. A favourite from those days was without doubt a place in the city center called A la Mort Subite. It was a favourite of my guide, & he reckoned was the traditional Belgian beer/cafe experience. Friendly service, no tourists in sight when I went there, however, was a few years ago now. An extensive beer menu!!
Here's a link :-
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Having travelled most of the country on a number of trips, the beer/food seemed much better in the south. & the folk friendlier!!