Small Town Getaway from Rome

Look at island of Ponza, train (*or taxi), then ferry.

Sperlonga is a great idea. Another island that is nice is Isola di Giglio, just off the coast at Porto Santo Stefano near Orbetello.

Note that technically it is no longer beach season in early September and some facilities may be closed. Once you have narrowed your search, ask a hotel you are interested in for advice.

Thank you for all of these suggestions! I guess I should add for further context, his family has a seaside home south of Rome we will be at for a few days so I was thinking a lake town to switch things up. But will definitely take a look at these options,

I got one for you. We did this in March 2017 with Roman locals that do this once every late winter or spring. It's not near water, but it's everything else and more.

Orvieto. https://www.passportandpixels.com/things-to-do-orvieto-italy/

An ancient Umbrian hilltop town a 90 minute train ride out of Termini station. You arrive at the station, then take the funicular to the plateau. From there, maybe my favorite cathedral in all of Europe, Duomo di Orvieto, is waiting for you. It sparkles in the afternoon sun. You wander the cobblestone paths from the 2nd century AD, do a little shopping, have a little lunch--fantastic cuisine, mix of Florence & Rome--spend an hour or two marveling at the cathedral's frescoes and the stories they tell, then you take the funicular back to the station, and the train takes you back to Rome. We dozed a little, then arrived back at Termini around 7PM...and it was time for dinner then a gelato!

A day well spent. Look at it.

Enjoy your planning!

Will look into that as well- thanks all!