Le Moissonnier is the best "bistro" in all of Germany. 18 points from Gault Millau and equal to any bistro in Paris. Expensive but not prohibitively so. You also should walk across the rail bridge and have a drink in the bar of the Hyatt. The view back across the Rhein with the bridge to the right and the Cathedral on the far side is one of the most beautiful in the world.
To be quite honest, I wouldn't go anywhere near Chinese restaurants in Germany. Most are too expensive relative to the quality, which is so-so at best. Why eat Chinese food when one only has a few days in Germany? That seems beyond pointless.
In addition to the suggestions hobsch made above, I also like Frueh am Dom and Peters Brauhaus for great Koelsch (both are brewery restaurants), traditional Rhein food (try the Sauerbraten, for example), and classic atmosphere.
For snacks, just walk into almost any bakery (Kamps is a reliable choice, among most others!) and try anything that looks good because it probably will be excellent.
So if you want some typical stuff try one of this places. I do visit them quite often.
1. Max Stark - typical brewhouse, cheap,very good food and Paeffgen Koelsch (maybe the best in Cologne), full of locals, close to the railway station and cathedral
2. Gaststaette Wirtz
Located in the "Suedstadt", also very good food - try the "Kotelette = Pork Chop"
3. Best Brauhaus = Brewpub is definitely Paeffgen in the Friesenstrasse, not too far away from the Cathedral. Located in a nighlife hotspot - Friesenviertel
All these places are definetely for beer drinking and German Food. Maybe they are too much smokers in there but it is hard to find a good place without this disadvantage.
If you need some other suggestions let me know.
Alright, it's 14 months later but I cannot thank you enough for the Max Stark recommendation -- two of the best nights I had in Europe -- crisp, refreshing beer, quality, fresh food (I had a massive pork cutlet one night, pork in plum sauce the other), VERY good service, nice crowd (lots of interaction) and chilled shots of Eversbusch, a gin-ish liqueur that was the PERFECT digestif. Two courses of food, LOTS of beer, mineral water, and two eversbuschs for less than 28 euros. Thanks SO much. Yes, people were smoking, detracted not all from such a vibrant and fun place.
If you are going to Cologne hit Max Stark -- easy and pleasant walk from the Cathedral or the station.
If you like beer, that is the home of a type of beer called Kolsch. I like Fruh very much (though I haven't had it in years), but Dom is good and there are a few other varieties. It's a very light beer, actually low in alcohol, but one of my faves (and I typically like darker or more full bodied beers).
There is a small but very nice restaurant in the Antonius Hooper Hotel - a very short walk from the Dom area. It had a great, neighborhood feel to it - very informal and good prices. A local friend of mine took us there. Take lots of warm clothes as it was bitterly cold the February we visited Cologne. The downtown area is full of small, interesting places so good luck and enjoy!
We had a blast in Cologne; Best meal we had was a chinese restaurant on a second floor in the downtown pedestrian area.
Had a sandwitch board on the sidewalk as advertising. European Chinese is different from American Chinese Be polite say Bitte and Danke,Please and thank you, and have a great time.