Cologne Bonn airport was a lot bigger than I expected, though I don't know why I felt like it would be a small airport. Upon arrival you see that there are a ton of parking options, with the cheapest option only being a five minute walk to terminal one. There are two terminals in the airport and terminal one is the more modern of the two. With plenty of places to shop and eat, you will not have a hard time making sure you have everything you need before your flight takes off. One thing we did notice was that even though we were at the airport at 8am, there were quite a few restaurants that we not open yet and we found that to be surprising. Overall, it's a super nice airport, security took less than five minutes and parking looked easy (we returned a rental vehicle and that was easy as well.)
Empfangsgebäude Bonn Hauptbahnhof
The train will take you to the airport so you don't have to worry about rental cars.