To Poros, you can go by travelling to Galatas and take the ferry ore one of the small boats (price 2016: 1 euro) across the narrow strait. The ferries take about a quarter of an hour and departs often. If you drive your own car, don’t bother to bring it onboard the ferry if you only intend to visit the capital of Poros, the ferry dock there.
The name Poros means strait in Greek, and consists, in fact, of two islands; the large, pine forest clad Kalavria and little Sferia, a volcanic island formed in 273 BC. Poros town is built on Sferia, and is connected by a bridge to Kalavria.
Poros town rises pretty and white like an amphitheater overlooking the Peloponnese. Walk up to the bell tower on the top and enjoy the view over the sea, island and countryside, visit the archaeological museum, and find a cozy tavern.
Galatas is located 69 km from Nafplio. There are buses between Nafplio and Galatas a few times per day, see KTEL.
Visit an island, or two, or three
The Argo-Saronic Islands Hydra, Spetses and Poros are situated close to Argolis, and are excellent day-trip destinations from Nafplio.
Hydra (above), Poros (below).
Hydra (also see main photo) is a car-free island (with the exception of two small garbage trucks), and the beautifully located city is very pretty and very well preserved. The bustling waterfront is filled with cafes, souvenir shops and tourists, but is still a nice place to sit with a coffee and look at the life and the boats - and the donkeys used for all transport on the island. You should also go for a walk in the picturesque and peaceful back streets, and find a tempting tavern for lunch. Beaches are not Hydra's strength, but you can walk to the other end of the dock in relation to where the boat moors, and upwards following the footpath, and soon you'll see a tiny rocky beach below you.
Hydra is currently quite dry and barren (despite its name that means water), but nonetheless it has its own beauty. During the summer weekends the island is full of Athenians who have summer homes here, and many tourists go for a day trip to the island.
Spetses has a nice beach in the capital, a ten minute walk from where the boat docks, but there is also a small beach exactly where the boat moors. Spetses’ town is not as beautiful as Hydra’s, but if you want to learn more about the war heroine Bouboulina, visit her museum. Bouboulina moved to Spetses when she was a girl, and she would later provide one of the most powerful ships during the Greek War of Independence. She sailed it from Spetses to Nafplio, and she and the troops she led took part in the siege of the city, which ended with the Turks giving the city back to the Greeks in 1822. She later fought for other Greek cities, but died in 1825, only 54 years old. One of her daughters married the war hero Kolokotronis' son.
Moreover, there are ferries from the southern Argolis, specifically from Kosta/Porto Heli to Spetses and Hydra, reached by bus from Nafplio, but it's not likely you can manage to go to an island and back in one day if you rely on public transport.
Poros (left) and view from Poros towards Galatas (right)