Poros Island, the Argosaronic.
By boat: Poros is well connected by fast services in the summer, with typically 3 connections a day by Hydro foil, three by fast Catamaran, and two by larger ferry, most of which ply the whole route from Piraeus to Poros, and on to Hydra, Ermioni, Spetses and Porto Heli.
Between mid October and Easter the service reduces significantly, with the regular ferry providing the main communications.
These services are all run by one company: Hellenic Seaways (www.hellenicseaways.gr). The car and passenger ferry from Galatas on the main land opposite makes the five-minute crossing every 30 mins.
Poros Travel Guide