On a recent trip to Greece we decided to get out of Athens for a few days, driving to Ermioni in the Peloponnese. We rented a car at the airport - Auto Europe - good experience. I’d purchased the 2013 Italy and Greece maps for my Garmin GPS and entered coordinates for our stops before we left home. Coordinates are good as there are several spellings for most destinations - just look up Epidavros and you‘ll see what I mean. I’m sure the route the Garmin chose was not always the best, but it kept me on paved roads and always got us there. We had a detailed map too, but never used it.
Driving secondary roads - most of them are secondary - is an adventure. I enjoyed it - my wife’s opinion may differ. The roads are narrow, but fairly smooth and there’s room to pass oncoming vehicles. Locals will tailgate you until you can pull over - you just get used to it. As you approach small towns, the already-narrow road gets smaller and frequently turns into a twisting single lane as you pass through town. At that point, it's good to watch the signs and ignore the GPS. Mine was recalculating every 100 feet. As you leave town, the road gets wider and the GPS finds itself. Some of the scenery is spectacular. The GPS route from Ermioni to Nafplio included a mountain pass with constant switchbacks where I seldom got out of 2nd gear on the uphill side. But distances are short, and we always got there soon enough.