Nafplio is the easiest good day out from Athens. Two and a quarter hours on a public coach, twelve buses a day in the week, and a fare that has not moved much in years. It was the first capital of modern Greece, it is built under a Venetian fortress, and unlike Delphi you do not need to plan the day around a single return bus.
Why this route is different
Most of the 62 KTEL operators publish a timetable and leave it at that. KTEL Argolidas publishes departures split by weekday, Saturday and Sunday, marks which buses take pets, and prints a fare table that matches what you are charged at the window. That is rarer than it should be, and it is why this is the route we can answer in full without ringing anyone.
What is actually there
The old town is small enough to walk in an afternoon: Venetian houses, a harbour, and the Bourtzi fortress sitting on its own island in the bay. Above it is Palamidi, reached by a staircase that people will tell you has 999 steps. It does not, but you will not be counting by the top. There is a road up if the stairs are not your idea of a holiday.
Mycenae and Epidaurus are both close, and both are served by the same operator. If you want all three you are looking at two days rather than one, and Nafplio is the obvious place to sleep in between.
Building the day
The 08:00 from Kifissos on a weekday puts you in Nafplio a little after ten, with the whole day in front of you and the 20:30 back if you want to eat there first. At weekends the earliest is 07:30, which is close enough. There is no need for the tight there-and-back arithmetic that Delphi demands, because there is a bus roughly every ninety minutes in both directions.
Book ahead in July and August. Argolida is a domestic weekend destination as much as a foreign one, and Friday evenings out of Athens fill up.
What it costs
€15.70 each way, €29 return, which is a saving worth taking if you know when you are coming back. Palamidi and the archaeological museum are ticketed separately and neither is expensive. The whole day, transport and entry, comes in well under what an organised coach tour charges for the same ground.