Hi Goldenhawk,
yes, indeed there is a heliport in the City of Cologne. It's placed on top of one of the buildings of the Cologne Fair pretty close to the Cologne Cathedral.
Since it's an elevated helipad, twins only. It's also PPR and no refueling possible. So you might want to go straight for the International Aiport (a little bit expensive though)
A good alternate would be a small airport in the south of Cologne:
EDKB (Bonn-Hangelar)
If you need more info just let me know.