One of the places you have to visit is Alexanderplatz. It is the site of so much history, in particular the Alexanderplatz demonstration on 1989, just before the wall came down. Over 1.5 million protesters gathered in what was the biggest protest ever in East Germany, so of course it was somewhere we had to visit.
But we were somewhat startled to find that we had stepped into a very large African market. We (purely by chance) selected Africa week to visit Alex, so the square was fulled with African goods for sale (think Greenmarket square or Long Street in Cape Town), and African bands playing on the stages. It was fun and entertaining, but not quote what we expected in the middle of Germany.