The formula 1 race track in the city of Spa is a splendid race track, and Michael Schumacher called it one the most technical race tracks in the world !!
I am no fan at all of Formula 1 so I never went to see it, although it is only 35 miles away from me, BUT it is also used as the starting place for the yearly belgian mountainbike GP for the world championship ; so I am there at least once a year !
Bigjake is right about one thing : the ardennes (southern part of belgium) is a beautiful area with lots of pine forests ! Too bad the dutchmen seem determined to invade the place for holidays.