After visiting Delphi, I want to spend 3 days on Peloponnese Peninsula, with Nafplio as a base. Is there a bus traveling from Delphi to Nafplio that crosses the Corinthian Strait near Patra? And are there good car rental agencies in Nafplio?
The simple answer is probably not, but maybe. There are few direct bus routes in Greece. You can usually go from city to city, then transfer at each city and finally make your way to your destination. So you might find a bus from Delphi to Patras, then to another city, then another and so on. And the country is notorious for not having good route maps and schedules. You most certainly wouldn't be able to make it to Nafplio in a day.
An easier answer is to drive from Delphi to Nafplio, especially since you want to rent a car there anyway. How are you getting to Delphi? It's an easy drive from Athens, and you can rent from the airport to avoid driving near the city center (not for the faint of heart).
The ride from Delphi to Patras is very scenic. And if going that way, you might as well stop in Olympia. But that would require an overnight in Olympia. Otherwise, you could drive from Delphi to Nafplio in a long day's drive (it might not look far, but most of the roads are very twisty).
Keep in mind that you must have an International Drivers Permit to legally drive in Greece. And most agencies do require it for the rental.
There isn't one direct bus. It would be possible to do it this way round changing at both Nafpaktos and Corinth.
There's a 13.15 bus daily from Nafpaktos to Patras which passes through Nafpaktos. Timetable here
The Delphi to Nafpaktos journey is around 2.5 hours so you should reach Nafpaktos in time to catch the 17.00 bus to Athens. Timetables
This goes via the Corinth bus station, which is outside the city, and there you can pick up an Athens to Nafplio bus.
We've done this route and it is very scenic. We weren't in any rush though and spent a few days in Nafpaktos on the way. To do it in one day is possible in theory but that assumes the timetables are up to date and nothing goes wrong! If it were me and I wanted to be sure of doing it in one day I'd go back via Athens.
Both Delphi and Nafplio are great so whatever you do I'm sure you'll have a wonderful time.
PS Just realised the timetables are in Greek! Even if you don't speak any it's easy enough to figure out Δελφοί (Delphi), ΝΑΥΠΑΚΤΟ (Nafpaktos) and ΑΘΗΝΑ (Athens).
Thank you for the two responses which illustrate the time involved in moving from place to place in Greece by bus. If we were brave enough to use a rental car for the entire trip, it would probably make the trip better. We are flying into Athens and want to rely on public transportation to move around. The start of our tour involves taking a train to Kalambaka, spending a few days at Meteora, using train and bus combo to get to Delphi, and after visiting Delphi, we want to spend 3 days on the Pelo. Pen. It seems that the easiest way to get to Nafplio is to return to Athens from Delphi, and take a bus from Athens to Nafplio. Even though we don't like to rent cars, it seems that having a car is the most efficient method for maximizing our time on the Peninsula. We wanted to enjoy the scenery on the Delphi-Nafpaktos-Patra route, but it may not be possible because of our time constraints. Thanks again for your insight.