Everytime I visit Berlin I cross the Alexanderplatz in Berlin Mitte, at least once. For me it's something like a center point from where you can reach all other places pretty easy. Even though it is kind of an ugly place, there are some spots worth taking a look - for example the "Urania-Weltzeituhr", an impressive architectural structure, showing all the worlds timezones on its 24 sides. The Weltzeituhr is also a very famous meeting point in Berlin.
For the Berlin-series I just used an old 50mm lens, with manual focus only. Topic is street / documentation.