The calculated distance (air line) between Ganghwa-gun and Kaesŏng is approximately 16 miles respectively 26 kilometers.
By car or train, the actual journey to Kaesŏng is certainly longer, as only the direct route (as the crow flies) between Ganghwa-gun and Kaesŏng has been calculated here.
Air line (approximately)
26 kilometers
14 nautical miles