I have never really thought about the public transportation system is so well developed in Berlin. I was quiet scared at first because I thought Berlin is like the United States, that if you do not have a car, you are stuck. Surprisingly, Berlin is one of those city really convenient to travel around, as the public transportation does not close till late (1：00 am?) and it opens so early. Stacy and I went to Paris in the early morning around 4:00 am, we took the tram, we came back like 12：00 am, we took the tram... It was madly crazy that knowing we still can save money without taking taxi. We loved it so much that we'd rather wait for 20 mins to take the tram to get back to the hotel. More importantly, unlike Paris, Berlin's transportation was really clean and easy to track, fairly new as well. I love the yellow tram, I will definitely miss M4, so many dark nights, it took me back home...