15 days in Greece

I might suggest skipping Hydra since you'll also be going to Santorini and Mykonos. That will also give you some time for the Peloponnese.

For the Peloponnese, Nafplio is an excellent base and worth a couple nights at least. Very quaint small city and very walkable. Nearby are ruins for Epidavros (intact amphitheater) and Myceanae (reportedly the ruins of King Agamemnon's city). It's an easy daytrip to the ruins of Mystras, a former Byzantine city just outside of Sparta (Sparta not worth visiting). Along the way between Nafplio and Athens is Corinth, which has some ancient and early Christian ruins. Olympia is further away and needs an overnight there if you wished. The ruins there are not overly impressive but there is something magical about being there. Good museum.

Delphi is also worth an overnight trip from Athens or can be done as a daytrip by public bus or on a guided tour excursion. Unfortunately it is the opposite direction from Nafplio but if you can fit it in, the site and museum are worth it.

I agree with Douglas on Hydra. Either that or skip Mykonos for Hydra. Either or. As for the Peloponnese, you might also consider Monemvasia or Kardemyli. I hope this helps some.

You don't say how many days you plan to spend on each islands. Agree the Peloponnese might be more to your liking than Mykonos, based on your likes above. One night stay is enough time to explore Hydra and see a hopefully beautiful sunset. We flew to Santorini from Athens - a great timesaver. If you spend 3-4 nights on Santorini you could ferry to Pireaus and then to Hydra for a night. That would leave you with 6-7 days for the Peloponnese and Delphi. Agree with Douglas about Nafplio and nearby sights. Monemvasia is great - we stayed off the rock in Gefyra with a great view of Monemvasia - and it's not too far from Nafplio. Have fun planning!

Thank you everyone! You are more or less confirming what I want to do. I think flying to Santorini after Athens sounds like a plan. Skipping Mykonos (not much of a night-life person) and heading back to Pireaus for a ferry to Hydra. I really do want to see it - maybe the donkeys? No cars? But from Hydra, would I have to go back to Athens to rent a car to get to Nafplio, Monemvasia and Kardemyli? Maybe if I did, I could do an overnight to Delphi and then down to Nafplio? From Kardemyli should I go back to Athens to return the car and fly to Kelaphonia (if that is possible)?

We rented a car on line from economycarrentals.com, but there are many companies to choose from. You can pick up the car at the port. We told then when our boat from Hydra would arrive and someone met us at the port with the car. He even drove us out of town and to the highway and took us to the least expensive gas station, as we got the car empty and returned it empty. We turned the car in at the Athens airport and took the metro to town, as we stayed in Athens at the end of our trip. You could probably return the car to another town, depending on how you're getting to Kefalonia. If you do plan to drive back to Athens you might have time to visit Delphi and spend the night there before returning the car. We had 2 weeks to spend but did a similar route staying in Loutraki (a beach town near Corinth), Nafplio, Gefyra, Kardamyli (1 night is enough) Olympia (1 night), Delphi, Athens. It looks like Olympic Air has flights to Kefalonia and it looks like you can take a ferry from Patra so depending on your dates and timing you could do either. Check this website for more info http://www.greeka.com/ionian/kefalonia/island/travel-kefalonia.htm. If you decide to fly, then I would suggest you save Athens for after the Peloponnese and fly directly to Santorini when you arrive in Athens. We did that and it saved one day as we were already in Athens when it was time to leave Greece. You could then spend 3 nights in Athens and fly from there to Kefalonia if the timing works. Good luck!

I suggest skipping Hydra, there are plenty of places to see donkeys, all over the Peloponnese and in Kefalonia. If you are dead set on Hydra, maybe do it on your last day in Greece. Leave your relatives a couple days early, skedaddle back to Athens & see some landmarks there ... then if you MUST, go to Piraeus and go to Hydra. (IMHO, Rick Steves emphasizes Hydra because his books and videos don't cover many islands, and Hydra is a possible day trip on one of his tours, or before/after ... no one else promotes it htat much ... after you've seen a few islands, and their lovely port towns, Hydra won't be such a thrill). Just my opinion, after visiting over 2 dozen islands.