Its can be easy to just stay in Berlin as a local and even as traveller. Many visitors overlook Potsdam during their travels to Berlin however Potsdam is a fantastic day trip to take from Berlin. Here you will be surrounded by palaces, gardens and rich German history. Potsdam HBF is only 30 - 40 minutes from Berlin by regional train and is 7euro for a return ticket. I would suggest walking from the train station to the old town square to take in the architecture and museums. From there I would walk to the Palace grounds to see the two palaces and to have a picnic in palace garden or parks. On your way back from the palace grounds you will come across the Dutch Quarter and Nauener Tor which is the food and entertainment district. Stay for dinner and drinks and watch the street entertainers before making your way back to Berlin.