Sermoneta is a charming medieval walled hill village, south and inland from Rome.
To get in, it will be necessary to take a car, whether it is your own car, a rental, or a taxi from Latina Scalo (the train station for the city of Latina).
Everything in town is walkable.
There is a castle at the top of the hill. Otherwise, it's not so much that there are specific sights as that the entire town is picturesque, pleasant, and relaxing, and there are beautiful views of the surrounding countryside.
The center of town is the Piazza del Popolo. Sit outside at a trattoria there, and have some lunch, drink, and chat.
During the summertime, area farmers burn the chaff, and the smoke wafts over the town. This is not a source of contagion, but make sure to bring allergy remedies if you are sensitive.