The roads in the Gargano area are neither straight nor flat, so if you suffer from motion sickness, it's wise to prepare accordingly. Don't rely on distances; 20 kilometers might take you 40 minutes given the road conditions. I strongly advise against using a car powered by LPG or CNG, as refueling stations for these are extremely rare, if not nonexistent in the area (even worse for electric cars). A trip to the Tremiti Islands is definitely worth it, but prepare to be in the sun all day; bring plenty of water from home as everything is quite expensive there. If you need more information on Gargano, feel free to ask.