If you feel like listening to some music, why not check out the 2007 edition of the annual Klara Festival (now until September 14)? The focus is heavily on classical music, but there are also jazz and other concerts. And for those of us who work late and can’t make it to Bozar for the evening concerts that start at 19h00 or 20h00, Klara offers good alternatives: Late night concerts starting at 22h00 and even lunch concerts at 12h30 on weekdays.
Prices are extremely reasonable: EUR 7 for lunch concerts, EUR 5 for the late night ones (or free if you went to the evening concert that same day). Evening concerts have a wider price range from around EUR 10 to EUR 70+ depending on the concert. (If you’re short on budget, just get the cheap tickets – the great thing about having Bozar as a venue is that all seats are decent, which is not the case in many other European concert halls, so take advantage of your stay in Brussels!)