Walk at Rosenburg Parks
For breakfast I usually go to the next supermarket and bought some bread and yogurt. Right around the corner from the hostel is an ALDI Nord which has a very similar offering as the one in Bonn. And just like the Generator Amsterdam, this one is close to a park. Breakfast in a park is much better than the expensive buffets in the hotel/hostel where "all you can eat" does not even remotely match the amount that I want for breakfast.
The park is rather large and has a castle inside it.