Cologne Bonn Airport (IATA: CGN) handles international and domestic flights. The airport is approximately 15 min by S-Bahn (local train) to the centre of Cologne. S-Bahn fare (ticket zone 1b) is currently €2.80 one-way
Düsseldorf International Airport (IATA: DUS) offers many intercontinental connections. Train ride from the airport train station to Cologne central station takes about 40 min.
Frankfurt Rhein Main International Airport (IATA: FRA) is the largest airport in Germany, served by all major international airlines. ICE (InterCityExpress) high speed trains connect Frankfurt Airport and Cologne central station in less than one hour. Standard one way fare is €58. If you book your DB train ticket online three days before your departure to Cologne, there are a limited number of seats at a reduced price of 30-50%. If you pay full price you do not have to take a specific train, but discounted tickets are restricted to the train on your reservation. Trains via Koblenz, which use the slower, yet extremely scenic route along the Rhine Valley, are also 30% cheaper. The ICE train takes about one hour, the slower more scenic route takes about two hours.
Cologne is linked with Amsterdam, Brussels, and Paris by Thalys and ICE High Speed trains. Additionally, Frankfurt airport (IATA:FRA) has direct service to Cologne and is within one hour by ICE trains.
Cologne requires all cars to have a "Low Emissions" sticker in order to drive around in the city centre (Low Emission Zone, "Umweltzone").
Plenty of motorways (Autobahns A1, A4, A3, A57, A555) lead to Cologne. During rush hour the streets are heavily congested, also due to massive construction of a new subway tunnel Nord-Süd Stadtbahn, crossing half the city centre.
For cheap parking, with quick connections to central cologne, use park and ride ("park und ride"). At some stations, parking is free when you present a validated transit ticket on exit.
A street map, also showing where you can switch into a KVB subway, S-Bahn or Bus.