No special access issues
While on the mountain road from Palaia Penteli to Nea Makri, pass the Karakanta fountain and after 1 km or so turn on the first dirt road on your right. This is a crossroad of 3-4 dirt roads and there is plenty of room to park there.
If you want to move on for the Iero Block, by car or on foot, keep on the slightly downhill road on your right and at the first fork take the right direction for another 500 m. The block is at the left side of the road.