How to visit berlin on a weekend

A friend of mine is going to visit Berlin soon. Knowing I have lived there a few years ago, she asked me for some tips. This brought back my happy memory of living and working in this exciting capital from 2010-2012. Berlin is a wonderful city to walk around. There is a lot to do and see, yet it is not too big. Many sights are pretty much within walking distance, and very well connected(the transport system works great!! Credit to German engineering ) Comparing to other big city like London and New York, it is dynamic enough that you never get bored, but never too busy that you feel hectic. You can easily spend month there. Below are the places I enjoyed during my time there.