there's no must, it depends on your own likes and dislikes, where you want to go.
however here's only a few suggestions:
* if you like listening to funny short stories and nonsense poetry and understand German, don't miss the Lesungen such as 'Surfpoeten' every Thursday at Mud Club (Mitte) or 'Reformbuehne Heim und Welt' every Sunday at Cafe Burger (Turmstrasse/Mitte)
* Check out Kreuzberg! Here (and in neighbouring part of town Neukoelln) you get the best Lebanese and Turkish Food in town along with a couple of good clubs, cafes and bars
* if possible, get yourself a bicycle and explore Berlin on your own
Fondest memory: When I came to Berlin for the first time as a 17yearold addicted to London, I swore to never come and live here.
However, after 2 1/2 years in 'Germany's one and only metropolis' I came to like living here, although the roughness of how people behave towards eachother over here really pisses me off at times...
The Pergamon Museum, Brandenburg Gate, The New Jewish synagogue, The Reichstag, The Ka De We Departement Store and see the Food Departement on the 6th floor, The Unter-den-Linden Blvd. The Kurfurstandam Blvd, Have Coffee at the Kampinski Cafe,Visit Potsdam. See the glass dome in the New Reichstag
Fondest memory: Nothing
Favorite thing: If you like art and architecture, my two main interests, then Berlin is the place! There is so much new and exciting construction going on there, especially in the east part of the city. Because of the split they seem to have two of everything when it comes to museums and music. Two (more actually) opera companies, two Egyptian museums, two fine arts museums etc. However, they are in the process of consolidating them. This is a busy city with a lot happening and you get caught up in it very easily. It is not a pretty city in my opinion, but certainly one of the most exciting cities to visit. Aside from the obvious, do not miss the food floor at the KaDeWa (I think that's right) department store. If you like food (who doesn't?) this is a mind boggler. Bigger and more varied than even Harrods Food Halls. Plan to have a glass of wine or champagne there and then choose from one of the many food stands to have lunch. It is the best.
Favorite thing: Red squirrels are rare sight in the UK where they have been displaced by their imported grey cousins from the USA. I saw this red squirrel in the Botanical Gardens in Berlin.
Fondest memory: O.K. i know you can't all do this but the heading does say 'fondest memories of Berlin' and one of mine is dinner with friends in Berlin!
Find some good friends, to go on tour with you! What you do, does not really matter... Something will always happen to you, just because you are here!!!
Fondest memory: The flair of the city!
Fondest memory: Seeing U2 in a great concert at 'Waldbühne' in July 2001. One of the best shows I have seen by them....
When we arrived it was midnight, the night between years!
The view from the plain was spectacular!
This one is from when we got back!