The castle is one of the key sights in Malmo, though it is not a traditional European castle as you might see in France or Italy (Castello di Fenis). Set near a park, and still surrounded by a moat the castle still has something of a factory vibe to it.
Inside is the Malmo museum. The museum is quite unusual as it is a pre-history museum. an aquarium, an art museum and the Malmö city museum. It takes longer to view than you expect, and with the variety there is something for everyone, but it is not going to take the place of museums dedicated to their speciality.
There are a number of excellent places to eat in Malmo, but Bastard is one of the best.