Of the things I have done of a tourist nature since I arrived in Berlin I think the Berliner Fernsehturm has been my favourite.
Among other things you can see the Reichstag, the Brandenburg Gate the Olympic Stadium, the Museum Island and the Potsdamer Platz. All of which can be seen from the tower’s 360 degree view. But for me the best thing to see was the difference in architecture from the buildings in the East and the West.
Tickets are about 10 euro each. There is also a somewhat expensive restaurant you can dine at.