Western Belgium has plenty of famous tourist sights like Ghent and Bruges, as well as the coastal beaches.
Ghent: Ghent is maybe my favorite town in Brussels. Take a boat trip along the river, sample the cuberdons (little purple candy that comes from Ghent), and hit up the Gravensteen castle. There’s a pretty interesting troll bar, if you like getting trolled. Note– the boat trips seem to vary in length and quality (I’ve taken the same one a couple times and had different results. It might be inquiring where you go / how long it will be before buying tix).
Bruges: Anyone who’s see “In Bruges” knows this city already — total fairy tale. The Basilica of the Holy Blood has a vial of Christ’s blood, which is put on procession in an Ascension Day parade. It’s a great town to wander around and explore the zany architecture. Also I recommend going to the Straffe Hendrik brewery — it’s got great food and a tour in an historic brewery (still operational). As demand grew, they built an underground beer pipeline to a factory outside of town. They also have great views of city from the brewery’s tower. The VIP tasting tour is worth it. There’s also a much larger tower in the city center that offers good views, along with a Dali museum.
Coast: I haven’t spent much time on the coast, so I won’t dwell on it too much other than to say Oostende and Knokke-Heist are the two spots many folks go for summertime beach getaways. I’ve heard the beaches around Knokke-Heist are a bit less crowded. Either way, you’re on the Atlantic ocean, so it’s gonna be a bit windy.
Westvleteren: One of the famous Trappist beers and considered to be the home of “the world’s best beer” (Westvleteren 12), driving out here is a nice road trip through the rural countryside. The abbey has a great restaurant and gift shop, where each person can buy two six-packs of their famous beer, along with other abbey products. If you want to buy more (or one of the cases), you’ll have to dial the beer phone and get an appointment — I’ve heard it’s a challenge.