Cantillon Brewery is the last traditional lambic and gueuze brewery in Brussels, still using spontaneous fermentation rather than modern industrial shortcuts. The working brewery doubles as a museum, with old equipment, cellars, and self-guided visits that explain how lambic is brewed, blended, and aged.
It is one of the city's best stops for beer history, especially if you want something more specific than a cafe crawl. Tastings are usually part of the visit.