3 to 5 days in Athens pre-cruise in November - how to get to other towns and which towns to choose?

From the Athens airport you can take a bus to the central bus station (1h 15m) and transfer from there to get to Nafplio (2h 15m). That’s where I would sleep before your cruise begins. In Nafplio you can visit the fortress and take day trips to Mycenae and Epidavros. Not sure if there’s public transportation to either place.

Napflio is a good suggestion. While you’re in the area, be sure to see Nemea, an ancient site with remains of a temple, a small but excellent museum, and best of all, an ancient stadium. It’s in better shape than the one at Archaea Olympia (original Olympic games), and features a unique tunnel that the athletes passed through to reach the track/arena. There’s even graffiti scratched in the tunnel walls from athletes, proclaiming their performance in their games. We had the place to ourselves in April, and assuming it’s open, you likely won’t see another soul in November.

If you rent a car, that’s probably your best option for reaching these sights on the Peloponnese Peninsula, and on your schedule. With a car, another option (or in addition) is Delphi, site of the ancient Oracle. It has temples and a museum, all located just a mile from the small modern town of Delphi. If you venture out that way, however, rather than spending a night in Delphi, I highly recommend the town Galaxidi, a short distance further west along the coast. None of this should be too stressful, and would let you see ancient (pagan) sights, but have a sufficiently easy time before the cruise starts.

Corinth is on the way between Athens and Nafplio. It has pre-Christian and Christian ruins, associated with St. Paul. Also a Venetian fortress up the hill. And the canal to see from far above. I don't think trains are ever an option in Greece, driving would be best if you're up for it. Here's an excellent source on many aspects of Greece travel. This website, under "Explore Europe," also has lots of good info.

If all you've seen of Athens is a tour from a cruise, you ought to consider spending more time there. Besides the Acropolis (nothing wrong with a second visit) and several excellent museums, there's Mars Hill where I think St. Paul also preached. And some wonderful Orthodox churches too.

I understand that Socrates taught atop Mars Hill, too.

I understand that Socrates taught atop Mars Hill

The Ancient Agora is where Socrates lectured, Mars Hill is where the apostle Paul preached.

From the RS home page there's a link to Guide's Marketplace. It is where the guides that work with Rick Steves are listing what they can do since there are no RS tours and they are trying to make a living. There is a second link there to Guides offering tours, and they are listed by country. There are 4 or 5 listed for Greece. We are working with one of the guides on a 6-day tour prior to our October Greek cruise. I'm sure they can offer you good advice and tours outside of Athens, either multi-day tours or one day tours. Since they work with RS Travel, I think you can relay on them for good advice.

I think the monastery town nearby you are thinking of may be a place called Daphni, a Byzantine monastery church in suburban Athens. I wouldn't call it a must-see in Greece, or even in Athens, but it has some nice mosaics and it sounds like that's the kind of thing that interests your husband.

If I had 3-5 days to kill before a cruise out of Athens, I would go to Hydra, an island off the Peloponnese, which you can get to by ferry from Piraeus (about 90 mins, if I recall). Once on Hydra, there are no cars, just legs and (if you must) donkeys. Forced relaxation, and we loved it.