Porto Germanos, Greece

Probably the most beautiful sea you will find near Athens is in Porto Germanos which is as far west as you can get in Attika. In fact it is in the Gulf of Corinth. There are amazing ruins nearby and the whole area is archaeological so besides the town itself there is not much development and for now lots of pine forests. You can get here by KTEL bus but it is better as a day trip with a car or taxi.