Berlin S Bahn Touristenticket. Section c is the area around berlin, including the town of potsdam, the sachsenhausen memorial site and berlin's schönefeld airport. Their writers are also pretty cool.
As such, it is one of the biggest public transport authorities in europe. Fare zone berlin c includes both the outskirts of berlin and the city of potsdam. In buses, fares are paid to the bus driver, in trams at machines inside the trains.