The closest international airport is Köln/Bonn (CGN) at a distance of 30 km. The next major international airport is Frankfurt/Main (FRA), at a distance of 140 km.
Further information can be found on the website of the Physikzentrum Bad Honnef: How to get to the Physikzentrum
Try to reach Rene Reifarth:
International: +49 175 4070537
Inside Germany: 0175 4070537