I wouldn´t recommend you to stay near the main train station in Hamburg. On one side it´s mostly department stores and office buildings, and on the other side there is a bad zone, small but with enough junkies and prostitutes to feel uncomfortable. One of my friends works nearby, every morning they walk 5 minutes across the place, and at 7:30 in the morning there is already something going on ...

But I like Hamburg. It has the Alster, and the boats along the Elbe. There are small cruises (one hour or so), but if you get a decent transportation map, you can go from the centre of the city to Blankenesse using public transportation boats. It is very funny, and all those huge cargo ships coming into the harbour. You might even be able to see the new super Airbus being built there (I would be afraid of flying inside that monster).

I will send you later the address of a couple of apartment rent services in Berlin. I don´t think that you need to be really near the train station, but near a metro or tram station will certainly help. That will increase your selection.

Kind regards, Covadonga Bilbao - Spain