First trip to Greece in late November/early December -- Athens plus what two other places?

Nafplio is the obvious pairing with Athens. A beautiful little town with a lot of good restaurants and within striking distance of Epidavrus, Tiryns and Mycenae. If I were you I’d probably limit myself to just Athens and Nafplio, especially given your interest in history and art.

As well as the obvious historic sites there has been a real burgeoning of new galleries in Athens in the last few years. For example

https://www.nationalgallery.gr/en/painting-permanent-exhibition.html

https://goulandris.gr/

https://www.snfcc.org/en

Have a great trip.

Alan

I agree with beautiful Napflion, surrounded by many antiquities. Also on the Peloponneasean Peninsula visit Byzantine Mystras. I would also include Olympia and Delphi.
If you want to visit an island, fly to Crete, base in beautiful Chania, explore western Crete.

How many nights will you be in Greece? If it's two full weeks, you certainly have time for a total of 3 destinations. I agree with the suggestion of Nafplio on the Peloponnese Peninsula. We spent 5 nights there and loved it. We visited Mystras; it is doable from Nafplion. It's my favorite ruin of all the ruins we visited on our trip.

I don't know what the islands are like in November/December, but we also enjoyed Santorini and Naxos. Santorini is beautiful and the views are stunning, and I think it's worthwhile to visit at least once. I highly recommend renting a car at least for a day. The island is beautiful with other interesting sites such as Akrotiri. I don't think it will be too crowded in November/December. Naxos is also wonderful and beautiful, less crowded and more laidback than Santorini. But it's possible Naxos could be closed up by the time you are arrive.

There is a small art musem in in Nafplio. But in 2018 I saw it on a Wednesday. Because it is closed on Mondays and Tuesdays. Nafplio is a good town. From there I took the busses to Mycenae and back, and then to Epidavros and back, on the same day. On the way back from Epidavros, I had to take a taxi from Epidavros to a certain cafe. The bus back left from the parking lot of the cafe. I went to Crete. But only for two nights and most of three days. I probably would have been as happy if I had skipped Crete and gone to Olympia in western Greece.