Six of us have one free day before our tour starts in Athens in May. We are going to hire a driver to take us for a 6 hour adventure. Where should we go? Corinth Canal and Old City along with Temple of Apollo? Nafplio? (it is a 2 hour drive each way). Any other thoughts? Is there an olive farm worth seeing? Our tour the following days includes Athens, Mykonos and Santorini and a wine tour.
With at least a 4 hour drive, going to Nafplio if you only have 6 hours may be too short and olive farms are too far away in the south and west of the Peloponnese.
Another option would be to go to Cape Sounio which is a little closer at 1h15 drive from Athens city center, preferably via the coastal road. Organized tours with drivers last 6 hours. It matches perfectly to the time you will have.
https://www.discovergreece.com/experiences/visit-magical-temple-poseidon-sounion
Here is a second vote for a day trip to Sounion. We went with our pre-teen daughters in 2012. We drove ourselves and if memory serves, it was a Friday. Leaving Athens was a traffic JAM!! But the temple at Sounion was lovely, on a cliff, and near a beach-side taverna. Check it out on Google images. We also went to Nafplio and Corinth (on different days) and I recommend these too, but you may not have enough time to really enjoy these.
I would head to Nafplio and Mycenae but I would add an olive oil and wine tasting stop.
I agree with Nick. Nafplion is one of the prettiest towns in Greece; the other one is Chania, Crete.
Skip the olive farms and see Nafplion.