We're flying into Paris and out of Athens 18 days later in June. It seems impossible to hire a car for whole trip and the train won't work for us. Anyone knw the best way to get a car for this kind of trip, through France, Italy, across the ferry to Greece, maybe with time in Turkey?
You're describing one of the most complicated car trips imaginable in Europe - picking up in Western Europe, going through Italy, crossing on a ferry, and then going from Greece to Turkey. Why on earth can't you take trains?
Be aware that dropping a car in another country can be expensive. The rental franchises may have to pay someone to go and retrieve their car. You can imagine what this might cost for someone to go from France to Greece to retrieve your car...
Just for giggles, I tried this route on Autoeurope. They asked for a phone call to their 24/7 number in Maine - 1-888-223-5555. Give them a call. Their humans are extremely helpful and solutions oriented.
That's an incredibly long drive, even for a span of 18 days! Could you elaborate on why "the train won't work for us"?
I'd suggest looking at a combination of public transit (which is generally faster than driving) and car rental in specific areas. For such a short trip, use of TGV or other fast trains would be good or budget airlines if necessary.
I suspect that if you stay with your original plan to start in Paris and travel "through France, Italy, across the ferry to Greece, maybe with time in Turkey", you'll be seeing a lot of Europe through a windshield with not much time for sightseeing.