Daytrips from Locarno

I liked Monza when I visited years and years ago, but the Villa Reale is not close to the train station, so you are looking at 2 hours one way to get there from Locarno. Not sure it is worth it.

If lake ferries are running, the Borromean islands are really, really worth it (even if it takes two-three hours to get there).
I have also heard great things about the Centovalli railway to Domodossola and back. Perhaps it is feasible, as a long day trip, to head to Stresa via that railway and Domodossola, then take the ferry to Isola Bella, and go back to Locarno by ferry / ferry and bus. This is just a thought, I have not checked feasibility!

I've been to Val Verzasca three times, though most recently in the 1990s. It's a beautiful bus ride up that valley. I'm not a hiker, but I think it would that would make a nice walk. It's best in the spring because there will probably actually be water in the little waterfalls--though with climate change, who knows. Check ahead of time on food sources unless you plan to pack a complete picnic of your own. There may not be much (or anything?) on offer, especially outside the peak summer season. Keep in mind the elevation gain as you travel up the valley. It may be a lot cooler than Locarno; if it's also wet, you'd want appropriate clothing.

I've also once been to Morcote. Cute town on the lake. Quite touristy (though I don't remember a bunch of Americans) even decades ago. Probably a lot livelier on weekends/holidays. I visited while staying in Lugano. It seems to me it would be something of a schlep from Locarno. I probably wouldn't head in that direction unless I had multiple things to do in the area or along the way, which it sounds as if you might.

I also really like the scenic Centovalli rail trip, which would take you in a different direction and probably wouldn't combine well with other things you are tentatively planning. The Centovalli area is a sort of back-of-beyond experience. For some reason the SBB website isn't working for me at the moment, but the Deutsche Bahn gives a travel time of just under 2 hours with hourly departures. I've never done anything in Domodossola except change trains and head farther into Italy, but photos indicate it has some attractive historic architecture.

Edited to add: Balso's suggestion of combining the Centovalli trip with the Borromean Isles on Lake Maggiore is great if the transportation schedules work. The islands are beautiful.

Thank you both. We had discounted the trip to Domodossola because the destination itself seemed a little "meh." Now realize it is about the train journey, not the destination, and the Centovalli Railway looks amazing. Perfect!

Also, taking out Morcote. Agree, too far for the payoff. Monza is still in, as our main destination is the Duomo, not Villa Reale, and the Duomo is right by train station.

We are right at that threshold of whether Sonogno to Lavertezzo (8.7 miles, mostly downhill) is doable or foolhardy. Would love to hear from others who might have done that walk...