We were in Nafplio a number of years ago and used it as a base to explore the surrounding area.
The town itself is one of Greece's prettiest filled with character and charm. We stayed at a "hotel" just a few streets uphill with nice views of the water and Boutzi Castle.
Lots to do right in town with the Palamidi Castle to climb, back streets, lots of great tavernas. Even the "new town" is quite good where most locals do their everyday shopping.
Went to the Farmer's Market plus all the archeological/historic sites nearby.
Even did a day cruise to Hydra/Spetses with Pegasus Castle.
We used the bus exclusively which worked out fine back then.
We now rent a car any time in Greece which I highly recommend if you want to see the more traditional and out-of-the-way Greece.
I've seen your website before, quite good.
Let's all hope we can get back to normal soon and plan on another trip to Greece!