You have two options for off road in Greece:

1)[Only registered and activated users can see links. ] This used to be the best off road map for Greece since it has 3 categories of dirt roads (main, secondary and 4x4), but all 6.xx versions have a serious bug, where some of the map tiles are connected (broken road connections) and it produces crazy routes or it's impossible to calculate any routes at all!!!
The img file is a "mapset" of a solid Road map and a transparent Topo map with height contours (100 m) and some pois-landmarks.
It's good to have it on your device just as an off-road alternative map.
Available only with latin characters.

2) [Only registered and activated users can see links. ] this is a totally routable map, on and off road, but there are no dirt road categories, all dirt roads are one category.
In some areas the dirt roads have better coverage than Anadigit's dirt road, in other areas Anadigit is better off-road.
You can search for cities, addresses and pois (Andigit cannot) and it has semi-transparent land polygons (forests, national parks, bogs, rural area, bushlands, Natura2000 etc)
It also has a DEM model (3D landscape) and height contours (10 m)
All the road and search data are the same with the greek road map Autodrive.
Available with english (latin) and greek characters.

If I were you, I would download both maps. I would do all my planning using Topodrive and when in Greece I would use Topodrive as my main map for navigation.
Up on the mountains (using Topodrive to go up there) I would change to Anadigit just for small routes using secondary and the even smaller 4x4 dirt roads. When it was time to "travel" to another place, I would change back to Topodrive for "proper" navigation!

The original TYP files in those maps, that define the way the roads and polygons are presented on your gps screen are not-not so good, so we have made some better with custom colors (roads and land polygons) and better road width. If you want I can upload the two maps with such custom TYPs that we use here in Greece.