The calculated distance (air line) between Cill Airne and Rathfarnham is approximately 160 miles respectively 258 kilometers.
By car or train, the actual journey to Rathfarnham is certainly longer, as only the direct route (as the crow flies) between Cill Airne and Rathfarnham has been calculated here.
Air line (approximately)
258 kilometers
139 nautical miles