Turku hosts many privately owned student restaurants all around the campuses. To get the student discount, one needs the official student card. Some of the restaurants are open during the evening times and Saturdays as well. Holiday seasons limit the opening hours, but they often serve themed lunches such as Chirstmas lunch and Vappu brunch.
Websites where you can find mosts the lunch options in one place (both in Finnish):
At Duke John's Cellar you can enjoy a refreshing cup of coffee or a delicious meal while visiting the museum. The Cellar is also the venue for historical food festivities.
Entrance from the front courtyard.