Short answer: anywhere in Greece. Once your booking is confirmed, you're free to drive throughout the country for the whole length of your trip. No host can limit which regions, cities, or islands you visit.
What's included
You can drive anywhere in mainland Greece and on the islands, and you can take the car on a ferry — to island-hop or to travel between the islands and the mainland. Where you go inside Greece is entirely up to you.
The two limits
Keep the car in Greece. Driving outside the country isn't allowed and isn't covered by your protection plan.
Stay on paved roads and use the car normally. Off-road driving and prohibited uses (such as racing or any commercial use) aren't covered, and you would be responsible for any damage that results.
Kilometres
Your booking includes a set kilometre allowance, shown on your trip details. Drive as far as you like within Greece; if you pass the allowance, the extra kilometres are charged at the end of the trip at the rate shown on your booking. In short: plan for distance, not for destination.
Bringing another driver
If someone else will drive, add them as an additional driver in the app so they can be verified. Once added, they're covered under the same protection plan — at no extra cost.
You don't need to share your itinerary. A host can't require your travel plans or restrict where you drive within Greece. If you're ever asked to, contact Sync support.