Any suggestions for day trips outside of Brussels?

Lots of great opps for a day trip outside of Brussels, especially if you're into nature. My wife and I are cyclists, and hopping on the bike and heading out of the city into scenic beauty has never been easier. Sometimes we follow the towpath of the Leuven-Mechelen canal and then beyond towards Antwerp. For a more challenging ride we might head south into the hills past Tervuren and Overijse. The country has an excellently laid out and well-signposted cycle network. You can plan your route on the internet and then go from junction to junction; you don’t even need a map.

If you're not into that much leg-work, then take a leisurely drive down to the Ardennes and take off for a long walk in the hills and forests. As you can see, there's lots of exploring to be done, and there's plenty of rich country hidden delights outside of the city.