The calculated distance (air line) between Ondarroa and Donostia / San Sebastián is approximately 22 miles respectively 36 kilometers.
By car or train, the actual journey to Donostia / San Sebastián is certainly longer, as only the direct route (as the crow flies) between Ondarroa and Donostia / San Sebastián has been calculated here.
Air line (approximately)
36 kilometers
19 nautical miles