The calculated distance (air line) between Hannover and Castrop-Rauxel is approximately 117 miles respectively 189 kilometers.
By car or train, the actual journey to Castrop-Rauxel is certainly longer, as only the direct route (as the crow flies) between Hannover and Castrop-Rauxel has been calculated here.
Air line (approximately)
189 kilometers
102 nautical miles