The only way to reach the Kerkennah Islands is by ferry from Sfax. The crossing takes about 70 minutes and the boat docks at Mellita on the western island. There are several departures a day in summer, fewer in winter; check the current schedule locally.
Cars can be taken on the ferry but most visitors do not bother — the islands are small, flat, and well served by infrequent buses. Better still is to rent a bicycle on arrival; most of the hotels at Sidi Frej have them, and the flat roads and short distances make cycling the ideal way to get around. Louages and infrequent buses run between Mellita, Remla, and Sidi Frej.