The calculated distance (air line) between Kostanjevica na Krki and Sežana is approximately 75 miles respectively 121 kilometers.
By car or train, the actual journey to Sežana is certainly longer, as only the direct route (as the crow flies) between Kostanjevica na Krki and Sežana has been calculated here.
Air line (approximately)
121 kilometers
65 nautical miles