This is a beautiful card that I think is issued by Swiss Post - like a first day cover, or a max card. The image on the front matches one of the two stamps on the back. The image on the front is called Swiss Attractions - Bonn. There are about 2200 people in Felben-Wellhausen. The town lies along the Thur River in north east Switzerland. Felben and Wellhausen were actually separate communities until they merged in 1983. 

Troisdorf is located about 20 kilometres south of Cologne and 13 kilometres north of Bonn. There are about 77 000 people who live here. It doesn't say in the article I read, but I will guess Troisdorf is a bedroom community with many of the workers travelling to Cologne or Bonn to work. 

A bigger than average card of the Post Tower - the headquarters of Deutsche Post DHL Group. Deutsche Post is the traditional method of posting mail. The DHL Group is for businesses that no longer use traditional mail services.  As one they handle mail communication, press services, retail outlets, and dialogue marketing.  The Post Tower is found in Bonn (of which Niederkassel is a part of their metropolitan area). It is a 162.5 m, 41 storey office tower. Construction started in 2000 and finished in 2002 and cost €78 million. Niederkassel is located on the right bank of the Rhine and has a population of 37 000. Bonn is 10 km south-west, and Cologne is 15 km north-west.

Bornheim is a city of 50 000 found on the west bank of the Rhine, with Bonn 10 km to the north-west, and Cologne 20 km to the south. Bornheim has a strong agricultural industry and is famous for white asparagus.