The calculated distance (air line) between Hŭngnam and Sinsang-ni is approximately 18 miles respectively 29 kilometers.
By car or train, the actual journey to Sinsang-ni is certainly longer, as only the direct route (as the crow flies) between Hŭngnam and Sinsang-ni has been calculated here.
Air line (approximately)
29 kilometers
16 nautical miles