Day trip from Naples

Personally, if I was already in Naples, I surely would spend time there and reap all there is to see in Naples (which would really take a number of days, not just a single day). It's not that the other sites you threw out are not interesting and great in themselves, but why go somewhere else when there's plenty to see where you are already? It's not clear how much time you have in total to accommodate any of these places, so my answer is without having that context.

Thanks, Agnes, I will get a an afternoon in Naples the day before. So I have a whole day to do whatever.

Look on TripAdvisor for things to do in Naples. There are so many beautiful churches with exceptional works in them, great archeological museum, and really interesting convent overlooking the Bay of Naples (Certosa di San Martino). Plus you can eat some amazing food and sample good pastries (I recommend sfogliatelle).

It's technically not fair to compare a busy city like Naples with the other much quieter places you mentioned (totally different size, scale, and feel), but the cultural facets of Naples just outweigh the other sites (which are of course preferable if you only focus on natural beauty and relaxation).

We have to assume that the group tour is going to either Pompeii or Herculaneum or both. Are you going to Sorrento already? The 1 1/2 hour, paved, downhill walk from Sant'Agata sui Dui Golfi to Sorrento is very enjoyable. You should investigate what you want to see on Capri (other than the shopping, of which there is too much.) I'd note that with the overwhelmingly pedestrian-only streets of Capri, and the Phonecian Steps, it's possible to get quite a workout during a daylight (limited ferry hours) visit to Capri. (Walking to the Villa Jovis really seemed like three sweaty miles uphill in BOTH directions!) I hear you can hike down to the Blue Grotto from above, check me on that. Grotto viewing only by boat, we skipped it. Positano is also very hilly, with hundreds of paved steps. Since you have to get to Amalfi to go to Ravello, you'll spend a lot of time using public transportation rather than more expensive taxis. Did you like the city of Salerno?

Some other ideas:
Caserta Palace
Ischia (maybe wilder and more hikable than Capri, haven't been there)
I think UNESCO WHS Paestum is maybe too far.
Cave of The Cumaean Sybill (haven't been there)
Pathway of the Gods

Thanks, Tim. I'll consider your ideas.

Thanks, Agnes. I'll reconsider Naples.

With just 1 day I would probably either do the Amalfi Coast or Capri.

I agree with the poster that there is so much to see in Naples that it seems like you should just do it when you have more time. I spent 1 day in Naples 2 years ago and it wasn't enough. I am now going back in June for 6 days and it's still not enough. I'm not someone either that wants to go to a million churches and art museums.

Dick, the Greek ruins and relatively small museum at Paestum are really special. When I went there on a day trip from Naples, I took a morning train one hour to Salerno, spent a couple hours wandering around both the new and old cities there, then another short train ride to Paestum. Went through the 3 very intact Greek temples, all several hundred years BC, went through the museum, spent some more time in the ruins during late afternoon light, then took a direct train back to Naples, arriving in time for dinner. Maybe you would enjoy that too.