I would recommend stopping at the hilltop Monte Cassino abbey when driving between Rome and Naples. It is close to the autoroute, commands magnificent views, was the site of a famous WW2 battle and has an absolutely stunning church and crypt. Parking was €3 and the abbey was free to enter. (There is also a museum with newsreel with €6 entry which we didn't have time for.)
Edited to add: There is a clean WC block in the top left car park with a spirited young lady attendant!