The calculated distance (air line) between Bielefeld and Castrop-Rauxel is approximately 62 miles respectively 99 kilometers.
By car or train, the actual journey to Castrop-Rauxel is certainly longer, as only the direct route (as the crow flies) between Bielefeld and Castrop-Rauxel has been calculated here.
Air line (approximately)
99 kilometers
54 nautical miles