A suggestion for an alternative stopover on the road from Athens to Thessaloniki. Thermopylae (hot gates), in addition to being the battlefield of the famous 300, are a free access spas and a great place to stay overnight or just for a short stop to admire the extraterrestrial landscape.
The road leading to the pool is a popular stop for truckers, just ahead there is a traffic police building, so the overnight stay is more than safe and always with company. I advise you not to stay in the open space where you see the campers here on the left, because it is used by trucks to turn around. Better to find a quieter spot, the possibilities are many.
[GPS N 38.794132, E 22.528361]