Berlin Metro

(Image source: http://www.visitberlin.de/en)

Berlin's public transportation is very convenient, and almost all tourist sites are reachable through public transportation. No check-in process is need for subway or light rail; passengers are required to buy tickets upon conscious. Of course, sometimes there will be a plain clothes officer to check the ticket. In public transportation, Berlin is divided into A, B, C, three areas. A area is downtown Berlin, it is surrounded by the light rail; From the railway to the boundary downtown Berlin is B area; About 15 km outside the Berlin downtown is defined as the area C, the state capital of Brandenburg Potsdam and Schonefeld Airport belong to the category of area C.