In reply to Neilday:
Hi Neilday, the website
http://kletternimnorden.de/ may be useful. Contains topos etc. and it's of course all in German
Anyway it's very close to Hameln. I haven't been there so I can't judge.
There is a guidebook "Klettern im Norden" but it's sold out at the moment and sadly I don't have a copy. You may be lucky with some library...
There is "Hallelujah Steinbruch" near Bielefeld:
http://www.klettergebiete.info/html/klettergebiete-teutoburger-wal.html
It's a dirty little quarry with some "one move" bolted routes.
Further afield there is some climbing near Warstein. I haven't climbed there but the rock looked nice and solid compared to anything near Bielefeld.
If you're short of a climbing partner get in touch, I have a car and I'm am willing to travel (on weekends).
David