Greece trip end of March (Spring Break)

Are you open to rental car? You could easily fill the time in Nafplio and environs.

Are you renting a car? On this trip I would head to Napflio first and spend three days there, including a day exploring Epidaurus and Mycene. You could easily visit Ancient Corinth as you return to Athens. I’ve not been to Delphi but people seem to like to spend the night in the town so as to visit the site in the morning before the tour buses arrive and the. Head back to Athens and spend the rest of the time there. This will take two of the four days you have for Athens.

You no doubt will want to visit the Parthenon and the Acropolis Museum so would suggest you look for a hotel in that area…there are lots. I like the Plaka area even though it is tourist central. Other good areas to explore: Monastraki and Ermou Street, Syntagma Square, National Gardens and the temple of Olympian Zeus. If time and if you are not museumed out, the National Archaeological Museum.

I recommend the Eyewitness Travel guidebook, Greece and the Mainland. It includes an excellent Central Athens map as well as a decent road map of Greece. Although I have not used then, I think the RS guide to Greece would be useful or the RS city guide to Athens.

Yup, Nafplio is your best bet for a second base, two or three nights. I'd recommend one night in Delphi but with your overall timetable you might want to do a day trip or just save it for next time. You don't have enough days to spend them moving your base too often.

Thank you for the recommendations. We will end up renting a car for sure based on your feedback. I think Athens and Nafplio are locked. I will do more research on Delphi to see if we can make that work too.

Nafplio makes a good base for exploring the surrounding countryside. It is also a destination on its own with Athenians often use for a weekend get away.

On the way to Nafplio or on the return to Athens find time to visit Corinth area. There are some great sites on the way. Ancient Nemia had sister games to Olympia and the stadium is still there. You can still run races. Ancient Corinth is also a good site but for me the site right next to it Acrocorinth is a must see. It is on top of a mountain with 360 degree views over the area.
The canal is a must but consider hiking along the west side of the canal will take you to what appears to be an abandoned machine gun nest, an abandoned rail line and bridge over the canal and on a rocky section of the path you can see scratches from the time they hauled boats across the land.

While Delphi is a great site it might be just too much for the time you have.
The major sites in Athens can be done quite nicely in 3 days
Here are some images
Nafplio https://www.flickr.com/photos/stanbr54/albums/72157632094108982

Corinth Area. https://www.flickr.com/photos/stanbr54/albums/72157711755443483

Stanbr, since posting this on 12/16, OP has discovered the Deluxe Elite Costa Navarino Resort on Western Shore of Pelopponese & favors a long stay there instead.... That post makes their priorities clearer. oh well.