If by car, use the highway Atill exit Ploče. From there, you will need another 2 hours drive through a beautiful scenery of the River Neretva valley, a short passage through Neum and a memorable journey through the town of Ston with its mediaval walls which date back from the Dubrovnik Republic. In Ston you can stop for delicious oysters and mussels before you continue for another 25 km before you reach your destination.
An alternative way is after you leave A1 at Ploče to take a ferry from Ploće to Trpanj (50 minutes across the channel). Once in Trpanj, you need just 20 minutes, direction Ston /Dubrovnik to reach your destination, through a most amazing scenery and wine routes along your way.
Up to you to choose, both options are recommended.