If you don't have a vehicle it will be difficult to make it out of the cities to, say the Trappist monasteries. Several (Chimay, Westvletern and La Trappe) have wonderful restaurants that serve amazing local food and of course the Trappist beers. Brussels is not my favorite city, but Cantillon, Moder Lambic and a couple other spots are worth spending a day if you enjoy sours. If I had my druthers I'd spend the whole time in Brugges. Wonderful restaurants and amazing beer bars in a beautiful old city. Cambrinus and Belgian Beertje are my favorite spots there.