If you are visiting Berlin, I would suggest you to pick a day and visit Potsdam. It is in zone C of Berlin and you can easily take the S-Bahn to reach the place. It is a very beautiful, peaceful and historic area with a lot of stories and heritage. You can go on a free tour with a guide who tells you a lot of interesting historical facts. The area has a small center with a shopping street filled with shops and cafes. There is a huge park with a nice lake, which is a great place for pick nick, or running. On the picture you can see the summer palace, which is not that attractive during the winter, since the garden is empty. But as far as I heard during the summer everything is green and beautiful.