crown comfort
12358
Two suggestions
I don't know much about Cologne, but know my way around in Frankfurt and Berlin. I don't think I have to tell you on "what to see", there are plenty of guides and it depends on what's your interest.
I can suggest two restaurants:
Frankfurt: The Goldman Restaurant in the 25hours Hotel at Hanauer Landstr.: It's a bit outside of the centre near the ECB but worth the trip (taxi).
Berlin: my absolute favourite: Il Calice, near Ku'damm at Walter-Benjamin-Platz
Both have excellent kitchen, but are still casual enough and not outrageously expensive.
PM me if you have trouble finding them on the Web.
CC