If you have the chance of getting outside Brussels, do. The somewhat cold architecture of Brussels can be supplemented by the Flemish historical towns of Brugges and Ghent. Brugges has been kept in its original state since its glory days as a trade town from the 16th century. While it is maintained specifically for tourists, this doesn't detract from its charm, with traditional houses and cobbled streets. The canal tours, done by starving students, give you a good general overview of the city and its major historical places. The quiet Beguin monastery stands in contrast to the bustling main square, where you can take a carriage ride. If you climb to the top of the bell tower, and if it's a nice day, you'll be rewarded with a view of this walled city. Since it was in both Protestant and Catholic hands, there are churches of both faiths to be visited. The Basillica supposedly holds a piece of cloth that contains Christ's actual blood. The cathedral holds a statue of the Virgin Mary done by Da Vinci, supposedly the only one outside of Italy. Also, if you are a fan of lace, this is the place to get it in Belgium. Shops line the streets with all sorts of lace wear for the discerning tourist. It is the Venice of Belgium, although it is not sinking!
Ghent, on the other hand, is a living, breathing city due to its large university population. The historical part of town has also been preserved like in Brugges, but there are more signs of its continuous use as a living city, like modern shops and more cars. It is larger than Brugges but contains the same basic elements, like the main square and cathedral. Overall, it is more livelier than Brugges, which can be quiet due to its lack of a real population.