Took a flight from Barcelona to Düsseldorf as it was a direct flight. Took the rental car to Cologne. There seems to be a lot more direct flights to Düsseldorf than direct to Cologne.
Stayed in an AirBNB in the Deutz area of Cologne, not far from Lanxess Arena and within walking distance of the Koelnmesse Exhibition Centre. It was a good area, Köln Arcaden a decent shopping centre close-by, lots of food shops and restaurants as well.