Category:Route Athens - Thessaloniki
About 10 km before Katerini (east), coming from Thessaloniki, there is an amazing service station there called Olympus Plaza rest area. Brand new, there are others from this chain in the Balkans and in Greece, check out olympusplaza.gr or google it for different countries. Serbia has some as well. It has a restaurant open 24 hours a day with free showers and free wi-fi. Staff are very nice and they don't mind if you sleep there. There are comfortable benches and it's warm inside. There is a station on both sides of the road.
Very close to here also there is this church-built-in-the-mountain-rock thing that is a touristy attraction in the summer but otherwise no one is there. You can still stop over there to see it as it is beautiful and you get to cross a river using a nice bridge to get there. It's just by the side of the highway and there is an underground passage way to get from the parking to it. Your drivers should know about it if you explain. Maybe also a potential place to pitch a tent or sleep at the church entrance etc. There is also a house there and a kind of canteen but were closed during a recent visit. It didn't seem like anyone lives there. Also before you cross the river there are some little wooden hut things they use to sell souvenirs from. Might be worth checking out if they can be opened for sleeping in.
After getting out of Athens suburbs, if you get a lift for around 60 km maybe, you will find an Autogrill service station. It is a big one about 10 km south of Inofyta, like the kind you see in Italy. It has a connecting bridge so you can change sides of the motorway. It's a good place to change rides.
Also south of Lamia, at KM 90 there is also a petrol station but it's not so big or inviting so try staying away from that one.