Hamburg is worth been visited. A nice town, special arrangements of buildings due to the many waterlines. Most bridges in a town in Germany. A lot of culture, specially musicals. Right now Dirty Dancing and Udo Juergens, soon Tarzan. And of course the famous and dingy Reeperbahn. Come to Hamburg for Salsa dancing, enjoy musical excitement and a nice drink in chilling environments.
Cologne is one of the cities where you can party and dance the whole week. If people like you, you get everything from them. Cologne inhabitants are a special kind of humans. They love you or they ignore you. But the origin ones are openminded and have that kind of humour you will love. Join them, meet them and party with them. you will love it. And of course Cologne has much much culture to discover as well.
I love Hannover, due to the nice city architecture, the offering of dancing salsa on tuesdays and of course due to the nice people living there. i found them openminded and heartly during my last trips through Germany.
Bitterfeld is an old industrial place out of the times of communism during black times in Germany. But today govenment and industry showed that it is possible to invest in future and offer local inhabitants to join future trends and economics. Nice area and a lot space to walk and discover the nature. Horrible but have to be seen living areas with thousands of appartments.