Salamis Island, the Argosaronic.
By boat: Car and passenger ferries make the 15-minute crossing between Paloúkia on Salamis and the port of Pérama (1), 8km to the northeast of Piraeus throughout the day and night: every 15 minutes from 5 am to midnight, and every hour thereafter.
There are also ferries every 30 minutes to and from Paloúkia and the main port of Piraeus (2), between 6 am and 5 pm: on Saturday and Sunday after noons the frequency drops to an hourly service.
There is a car-ferry connection from the western end of the island which crosses every 30 minutes, between Stenó Phaneroménis (3) and the harbour for Megara, also confusingly called Nea Péramos: this then connects easily with the main Athens to Corinth highway.
If you require your own car on Salamis, which is necessary for exploring the island properly, it is advisable to rent from Athens, since there is no obvious rental facility on Salamis.