Yep, unfortunately to a non smoker like me it feels like it's almost compulsory everywhere in Cologne except on the U-Bahn where there are non smoking signs displayed but ignored by a lot of the teenage population out there.
We went to Phantasialand for the day & had to share ques for the rides with smokers.
If you go into a bar or a restaurant you will be greeted with smoke whether you like it or not.
I asked for a non smoking table in a restaurant near the Dom & was told that there was no non-smoking section in the restaurant, despite its size.
The food court in the station did not seem as smokey so we ate there & drunk our beers in the hotel bar.
One of my workmates who is a smoker told me that Berlin is totally different & they cater for both smokers & non smokers.
The Uk is gradually bringing in a smoking ban in all pubs, clubs & restaurants but as far as i know, mainland Europe does not have plans to follow suit.
Do not let that put you off Cologne as it's a fantastic city to visit with very welcoming & friendly people who will make every effort to speak English if your German isn't up to scratch.