Groningen seems a lot like a small Amsterdam, except students are substituted for tourists. When not trying to get our daughter settled into her university housing, we spent a lot of time mostly strolling around. There are a number of parks not too far from the city center. It was an easy walk to one park which had a music festival going on.
Like Amsterdam, Groningen has canals and a lot of time can be enjoyably passed crossing over canals and wandering along narrow streets with medieval buildings lining the sides. Many of the oldest buildings, scattered around the town, are part of the university which was founded in 1614.
One old building we stopped at had been turned into a pub. Because this is a student town, there are lots of pubs with very reasonable prices for drink and pub food, mainly sandwiches. The Dutch seems to love ham and cheese; we found it on almost every menu, including breakfast.
The Groninger Museum is a contemporary art museum in a building which is a visual curiosity on its own with its colourful tiles. We had a good cup of coffee and croissant in the museum café.
The center of the city is a no vehicle area, except for the big delivery trucks and of course, bicycles, which means you cannot exactly wander with your eyes looking upward and ignoring the possibility of getting run over. The Martini Tower dominates the central square, the Grote Markt, and provides an orientation point when aimlessly wandering.