Civitavecchia to Orvieto

You can do it via train for less than three hours and 15 euro. The cruise ship docks close to the train station. I am not aware of any real mountains in that area but I live in the Rocky Mts so I may have a different perspective. If you need a car, rent it after you get to Orvieto.

https://community.ricksteves.com/travel-forum/italy/car-route-options-rome-to-siena

We enjoyed a few hours in Viterbo on the way to Orvieto. Steep hills and scary James Bond driving do not occur on this route. Tuscany may be less green in November.

You need to consider the regular car annoyances in Italy, ZTL, IDP, and insurance, not to mention rental costs. We used Google Maps to find an agency just steps from the pier to shore (required) shuttle bus stop. Reservations essential. We booked a return to FCO. The highway trip to Sinalunga-FCO was long and not glamorous. Others have stopped at Etruscan tombs or other spots on the way out of Tuscany.

Orvieto has a massive, Mall of America like garage, with escalators to the town. Parking is harder elsewhere in Tuscany, especially in season.

The route is largely flat through the valleys. It's a two lane road, so speeds will be limited to 70km/h (45mph) or less inside built up towns. You'll hit some curves on a hilly segment with some switchbacks as you get closer to Orvieto, but no more than 5 miles.
It's almost two hours' drive.

Along the route (only a slight detour) there is the famous Civita di Bagnoregio also to consider. Lago di Bolsena is also nice.

The other options are nice, but for me Orvieto easily wins on quality and number of sights. It's not just a picturesque town.

However, if this a port-day excursion rather than your first land-based overnight after a cruise, it seem quite far to go, given that you'd have a drop-dead time by which you'd have to be back in Civitavecchia.

acraven brings up a good point. If this is just a day trip from a port stop, you wouldn't have any time once you got to Orvieto, especially when you factor in the time to rent the car and return it.

Yeah, I missed that. We rented the car mentioned above upon disembarkation. There is considerable risk in taking an independent train ride to Rome for the day, but it's faster than Orvieto. You need a closer target if you refuse to pay for a ship excursion. Viterbo is not remotely as lovely as Orvieto, but it's a heck of a lot closer.

I'd add that I found the walk between the port and the train station to be long and annoying. And when we got onto the correct shuttle bus for our ship, it then waited (with the engine and air conditioning turned off) for at least 20 minutes for other company passengers. We barely got to our ship in time. There are potential events that are not under your control, no matter how may guide books you buy.

Civitavecchia is famous for its remoteness from Rome. That's just how it is. Venice (now), Berlin, Granada .... they're all "cruise ports" that are not where your ship docks.

Thanks for all your input and suggestions. We will be in Civitavecchia on November 1 which is a business and religious holiday in Italy thus we want to avoid Rome. We have looked at various shore excursions, but are thinking that a rental car might allow for more time in Orvieto. Or maybe we’ll just save Orvieto for another trip when we can stay overnight, and just rent a car and go to Viterbo and Tuscania (less driving).

I've been to Tuscania and Viterbo; both are picturesque. You must research driving regulations before your trip. Both towns probably have areas where you are not allowed to drive (ZTLs). You need to know where they are and be able to recognize the signage instantly. Otherwise, you could receive multiple very costly traffic tickets (and administrative fees from your car-rental company) after you return home.