The calculated distance (air line) between Dortmund and Katwijk aan den Rijn is approximately 138 miles respectively 222 kilometers.
By car or train, the actual journey to Katwijk aan den Rijn is certainly longer, as only the direct route (as the crow flies) between Dortmund and Katwijk aan den Rijn has been calculated here.
Air line (approximately)
222 kilometers
120 nautical miles