Getaway by car?

How about Normandy. Just under 500 km from Brussels
Nice nature both inland on the peninsula and beautiful coastline and plenty of interesting sights. D-day, Bayeux, Mont St Michel

Baie de Somme, northern France: walking, food
Alsace: wine, food, countryside
Zeeland, NL: watersports, lots of fresh air

The Grand Duchy.

Bavaria.

Rhineland.

Well depends what you like doesn't it? Plenty of nice places to visit in France Netherlands Germany and still in Belgium all driveable.
Why don't you decide how long you want to travel for draw a circle on the map and stick a pin in as likely to get a places you like as asking a bunch of random strangers

To CC_R. That is a bit of an unhelpful answer isn't. The question is asking for specific recommendations. You are not responding, but just stating, plenty of nice places. So which, where? and then you finish it off by making a smart-alecky remark. If you can't provide a real answer, why do you even bother to respond...

Superb! Try a countryside experience at the B&B Koperen Pomp.
http://dekoperenpomp.be/
+32 (0) 470 89 03 93
dirk.zegers1@telenet.be