Hullo John,
The first thing that comes to my mind is the amazing Etruscan Necropolis in Cervetery, known as "La Banditaccia": imagine a funerary site filled with grass-roofed monumental tombs : one would take it for a hobbit town didn't you know it actually is a necropolis.
This is google+ page for the Necropolis
But the direction are not very clear there, you may want to check this Civitavecchia Tourist info page, maintened by the local community and therefore quite reliable.
Other very nice places in the area, but you should have the whole day at least to visit them properly as they are not exactly next to the airport highway are: Bracciano Lake or the Santa Severa Castle, also known as Odescalchi Castle, right on S.Severa beach, where you can spend very enjoyable hours (although it is absolutely packed during summer, let's say June to September) and visit a nicely instructive museum of navigation.
Hope this could help. If you have any further question please DM me.
Cheers
Javier