The calculated distance (air line) between Koksan-ŭp and Songnim-ni is approximately 55 miles respectively 89 kilometers.
By car or train, the actual journey to Songnim-ni is certainly longer, as only the direct route (as the crow flies) between Koksan-ŭp and Songnim-ni has been calculated here.
Air line (approximately)
89 kilometers
48 nautical miles