The calculated distance (air line) between Recklinghausen and Castrop-Rauxel is approximately 6 miles respectively 10 kilometers.
By car or train, the actual journey to Castrop-Rauxel is certainly longer, as only the direct route (as the crow flies) between Recklinghausen and Castrop-Rauxel has been calculated here.
Air line (approximately)
10 kilometers
5 nautical miles