We will be in Nafplion for six days in May. Any suggestions for day trips would be appreciated.
Oh, what a great prospect! Certainly you will want to plan day trips to Mycenae and to Epidavros. You can easily take the bus to each of those places should you need transportation.
I second the idea of Mycenae and Epidavrus, both great sites.
Nearer at hand, and little visited, is an interesting site at Argos. we've written up our visit there, with a few photos
It can easily be combined with a visit to Tiryns 'of the mighty walls' (according to Homer) which is halfway between Nafplio and Argos.
We've also written up our favourite restaurants and walks around the town, which you might find interesting
Have a great time
Thank you Sue and Alan for your suggestions. Alan's websites are excellent and most appreciated.
You might consider a day trip to the island of Hydra, which is touristy but rather unique since there are no cars. If you have a car in Napflion, you might consider driving to Metochi and then take the "Freedom Boat' ferry across the water to Hydra--the crossing only takes 12 minutes. If you don't rent a car, Pegusus Tours offers a boat connection from Tolo to Hydra a few days a week. Tolo is a port near Nafplion that you can get to by bus or taxi.
I assume you will have a car, getting around outside Nafplio without one is difficult. Six days there is more than enough to it will be easy to fit in daytrips, and there are plenty of options.
A few other ideas (the previous two are excellent and standards):
Mystras - an old Byzantine city just outside Sparta that was abandoned and fell into ruins. Think of it as the Byzantine/Greek version of Pompeii. Stunning scenery as it was built on a mountainside and still has several intact Byzantine churches and a monastery. Though Sparta doesn't have much ancient character, you can check out museums and ancient sites there too.
Monemvasia - a long day trip but another stunning Byzantine city. This one sits on a rock outcropping and is a functioning town. Think of it a little like Gibraltar and Mont Saint Michelle combined.
Corinth - Has an ancient ruins area and of course is famous from Peter's letters in the Bible.
Those trips to Hydra are handy, but the Original Poster is going in May, off-season, and I don't believe they are available at that time, at least not the Pegasus tours.