The calculated distance (air line) between Esplugues de Llobregat and Castelldefels is approximately 9 miles respectively 15 kilometers.
By car or train, the actual journey to Castelldefels is certainly longer, as only the direct route (as the crow flies) between Esplugues de Llobregat and Castelldefels has been calculated here.
Air line (approximately)
15 kilometers
8 nautical miles