Seeking 4 days in small city/town with access to nature—without a car!

It'd be a shame to be 70 minutes from Rome Termini by train (from Orvieto) and not visit the most important of cities. There are certainly enough sights in Rome to take the whole balance of your time. And yes, Rome is a safe city for single ladies.

Thanks, David!

I should mention that I’ll be spending the first day/night with family in Rome, and while we’re in Orvieto we’ll be doing day trips to other cities like Florence and Siena. I live in a big, busy city and love the outdoors, so I’m looking for some solo time away from the hustle and bustle of a major metropolis, a place where I can have some quiet time and enjoy some nature (without needing a car). Is it possible to find that in Rome (either in the city itself or through day trips), and if so, what are the areas I should seek out? Thanks again, really appreciate the feedback.

Ortesei in the Dolomites

Since you are flying out of Rome, I would just go there. You may like Trastevere, it is quieter, quaint, and safe.
For outdoors stuff, there is Villa Borghese, one of the largest parks in Europe. https://www.rome.net/villa-borghese

Appian Way
https://www.ricksteves.com/watch-read-listen/read/articles/time-travel-on-romes-ancient-appian-way

Ostia Antica (wander the ruins) or go to the beach there. Quick metro ride.

Cinque Terre has it all - but with hordes of tourists, so that might be the sticking point. I haven't been, but you could look at Lago di Bracciano. Bracciano has a bus or train to Rome (under 1 hour), but I don't know about public transport getting around the lake. It might be a bit further off the beaten path than you want. Viterbo is between a couple of lakes, has nearby hotsprings, an old Roman Road, on train and bus lines. Or just head to Capri.....though a longer trek from Rome.
It might depend on what you want. Is the town of more interest, or a hub for day trips?

The Protestant (non-Catholic) Cemetery is a peaceful place, very green. Not large enough for hard-core hking, of course.

I happen to be reading an Italy e-newsletter, and personally, have had an interest in the etruscans. Tarquinia is close to the ocean and has an interesting history. The land around looks more agricultural, but it could be of interest. Here is the article https://www.wanderingitaly.com/history/etruscan-civilization.html

You might look at the Parioli district of Rome. It's between two huge parks, so you'd have your choice of those areas or going "downtown" for other Rome sights. We stayed in Parioli one year and really enjoyed it. Castel Gandolfo might make for a lovely day trip.

Pitigliano is near Rome and has some fascinating Etruscan "vie cave" in the surrounding area. It would be a steep walk back to town, but there are trails.
I did not stop in Grosseto, but also in that region is Orbetello, and from there you could walk/bike to sandy beaches and take a bus to the rocky beaches of the neighboring promontory, catch ferries there too (for a day trip to Giglio). Check ferry schedules for Oct. though.

Perugia or Assisi

Give this web site a look, https://www.apathtolunch.com/, these folks have good information on the site for what you may be looking for. It is an interesting site to click around on a bit to see what may interest you. I gleaned a hike up Punta Manara while in the Cinque Terre area (Punta Manara is up north a few stops at Sestri Levante) and it was a really cool hike. This is kind of an out of the way hike IMO. There are many hikes in the area around the Cinque Terre so you can stay out in nature very easily. We stayed out of Cinque Terre at a great little town Moneglia at a wonderful B&B http://www.sussurridimare.it/. We were there in early October and the weather was great. We did not have a car, used only the trains and our B&B hosts for a few drop offs. Lucca would be cool for a couple of days also for a single person wanting to stroll around a bit. We hired a lady to give us a walking tour in Lucca and it ws really fun provided great insights into the walled city!

Thank you all for the very helpful responses! I’m looking forward to researching these suggestions further. :)