The calculated distance (air line) between Hennef (Sieg) and Karlsruhe is approximately 132 miles respectively 212 kilometers.
By car or train, the actual journey to Karlsruhe is certainly longer, as only the direct route (as the crow flies) between Hennef (Sieg) and Karlsruhe has been calculated here.
Air line (approximately)
212 kilometers
114 nautical miles