Castle park Sanssouci is the undisputed highlight of a day in Potsdam. The suburb of Berlin has its beautiful and its ugly sides, but Sanssouci is a must-see, especially in summer.
The park then blossoms, especially the often photographed wine hill near the castle. Don’t forget to visit the university: despite it’s vast size it is hidden behind the Neues Palais on the edge of the park.