Let's have a walk in the wild.

Jeremiah Johnson made his way into the mountains. Bettin’ on forgettin’ all the troubles that he knew… Lucky him! You can't wait to explore the wild near a lake, in a park or a forest? Well done! You've found us! You're by far the best trapper ever. YWe now how much you need your pine for the wilderness for a breath of fresh air.
Your plan: Nordic walking in the morning, picnic for lunch, hiking in the afternoon. If you enjoy city-trips, you need at least something green at hand and Bruxelles has parks and gardens to offer. No need to have an eco-friendly soul to understand that leaving your house can be very pleasant: get some fresh air, have a swim (preferably in the summer so you don't turn into a snowman), have a walk, feel and smell the surrounding nature, observe a flower. All these things are what make people happy.