The museums of Berlin are pretty good, so good that some you have to buy tickets in advance while others are a bit dark (Stasi Museum anyone?).
But I saw an exhibition on Europe and the Sea that turned out to be very interesting and tickets were available on the door. It told the relationship between Europe and the sea via some of its major ports over the last few millennium, including:
This one was clearly the wrong colour:
As well as examples of cultural elements, maps, navigational tools (top) there were also some good quotes, from Homer to Sir Walter Raleigh:
Very interesting, worth a visit if you're in Berlin.