It only takes 30 minutes by regional train from Hamburg to Schwerin, so it’s an ideal day trip. The homepage provided me with a tourist map where each POI is marked. There were over 40 marks, with the most important undoubtedly the castle of Schwerin. There was some construction work going on at that time, but the garden wasn’t affected. The castle is situated on an island and is the seat of the parliament of Mecklenburg-Vorpommern.
There are various lakes around the city. On a nice summer day, you can even see a rainbow: