Treptow is best accessed by S-Bahn lines S45, 46 and 9. The most important station is Treptower Park. To get into Kopenick take the S46 to Spindlersfeld or the S3 to Kopenick and consider taking one of the many trams to the old town and the old palace.
Perhaps the most picturesque line in the city, known to transit system officials as "the most beloved tram line in Germany" due to its customers' passionate opposition to reducing service, is Line 68. In off-seasons it has more scenery than people, but when hot weather comes its lakeshore meanderings and the tiny, "gemutlich" village of Alt-Schmockwitz at the line's outer terminal draw so many customers that extra trams are pressed into service. Line 68 may be best accessed at the Berlin-Grunau S-Bahn station, where all types of convenience food and shopping are available.
Beyond the village center and tram terminal, a large forested area of lakefront parkland offers hiking and bicycling possibilities. This was once the home neighborhood for expatriate American, international music and film star Dean Reed. The Line 68 tram itself had one brief moment of glory, in 1936. In its former incarnation as Line 86 it was the best route to the Olympic rowing events and some structures, street names, etc. still reflect that high point.
'''Mueggelsee''' - Berlin's biggest lake. You can travel there by tram which is an experience by itself.