Berlin is an amazing city, and I did not think I would like it so much. There is everything you need - culture, festivals, gardens, historical monuments, museums ... it is a very nice city. It is 8 times the size of Paris, so you have to be prepared to walk a lot. The center is organized around the Mitte district and the Museum Island (most of the museums are concentrated there, it needs at least a day if you like art). Then there is a notable difference between what was West Berlin and East Berlin. You can see it at various points. I recommend you spend a couple of hours also at the museum of the Wall.