Nice way to pick a city. :) And pretty nice how you describe it, too.

However, be glad you didn’t see the cathedral in daylight. – I see it every morning when commuting to work, and finally decided it’s quite nasty. ... We’ve got an ongoing discussion here on whether the muslims shall be allowed to build a quite large mosque with high towers, and on the other hand there’s the cathedral and the UNESCO’s demand that there may be no other building around topping the height of the cathedral.

My conclusion was, the cathedral is a real logo for Cologne. But why shouldn’t be there any other? Like a mosque? Cologne has so very many churches, it won’t hurt, I think. And, maybe, they might manage to keep the mosque’s stone white. I think, for the cathedral, they’ve given up that one already. The stone’s getting black so quickly, you almost can see it going on. It’s because of the exhaust gas of the cars.
 

Another hint for diving into Cologne might be to “surf a couch” of someone living here. There’s a quite active Couchsurfing.com group around for the Cologne/Bonn area. Although that community does not belong to Robot Co-Op (43places etc), I suggest to take that chance very much. Once, I surfed a couch in Braunschweig and it was a great experience and chance to learn about that city and city life.