Cologne-Bonn Airport is located between the former West German capital of Bonn and the larger city of Cologne. It's a major international airport, with good rail links to all parts of Germany. Eurowings and Ryanair both provide direct flights from the UK. As well as being the ideal place to fly into for any games in Cologne itself, it's also not far from Düsseldorf (1 hour by train) or Dortmund (1 hour 35 minutes). 

You can get from the airport into the city centre (Cologne main station / Hauptbahnhof / Hbf) in just 10-15 minutes and, if arriving on matchday, could get straight to the RheinEnergie Stadium in about 45 minutes. 

My suggested route from the airport to the stadium would be: S19 S-Bahn (metro) heading for Düren Bf. Get off at Köln Weiden West. Switch there to the U-Bahn (underground) and take the U1 heading for Bensberg. Get off at the stadium stop, called Köln Müngersdorf RheinEnergieSTADION (see the KVB Cologne public transport site for details).

If you have a rail pass such as Interrail (valid for trains and S-Bahn, not the underground) or the Deutschlandticket, you're covered in terms of the fare. If not, it might be worth getting a KölnCard for free 24 or 48-hour travel on local public transport, plus discounts to many attractions.

If you're planning to pick up a hire car from the airport, the better-known rental companies based there are Avis, Budget, Enterprise, Europcar, Hertz and Sixt. You can see which offer the best prices here at Rentalcars.co.uk.