The calculated distance (air line) between Ongjin and Yonggang-ŭp is approximately 64 miles respectively 103 kilometers.
By car or train, the actual journey to Yonggang-ŭp is certainly longer, as only the direct route (as the crow flies) between Ongjin and Yonggang-ŭp has been calculated here.
Air line (approximately)
103 kilometers
55 nautical miles