Karystos
From the airport in Athens, a bus goes to Rafina by the ferry. You can buy the ticket on the bus. The bus stop is located directly across from the car rental company when you walk out of the airport to the right (about here). Departure times can be found here or here. You can view the webcam from Rafina Port here.
If you are coming from Athens, the bus leaves from this stop to Rafina. The metro station is called Nomismatokopio.
From Rafina, you continue by ferry to Marmari and then take a taxi to Karystos. Ferry departure times can be found here, here, or here. If there is a long wait in Rafina, there are lockers for your luggage. In Karystos, we will be waiting on the Tinker.
It is also possible to take the ferry from Agia Marina to Nea Styra. The ferry operates quite frequently. Especially in the off-season, it is a good choice.