By railway : Deutsche Bahn
from south: Siegburg/Bonn station (17 minutes by taxi)
from north: Bonn-Bad Godesberg station (2-minute walk)
Scanned streetmap: As you can see our office is very close to Bonn-Bad Godesberg station, it's just a 2 minute walk.
By plane: Fly either to Cologne/Bonn airport,
capital of Low-Cost-Carriers (20-30 minutes by taxi) or
Frankfurt (Main) airport
(37 minutes by train to Siegburg/Bonn + 17 minutes by taxi) or
Düsseldorf airport (45 Minutes by taxi or train)
Here is a general timetable from Expedia and links to Lufthansa, Air Berlin, Germanwings and TUIfly.