Just checked this .....
Metro Line 3 connects the airport to the city centre (Syntagma Square). The journey time is approximately 40 minutes. Trains run every 30 minutes, 7 days a week from 6:30 am to 11:30 pm. One way tickets cost €9 (€4.50 for children, teenagers, over 65), return tickets...
When you get to the train station at Athens there's a pretty big ticket office (on the left hand side as enter the station)
I've always bought my train tickets there rather than use the machines - staff are used to tourists and speak excellent English - although a please (parakaló) and thank...
Good idea.
3 of us on flying out of Stanstead on the Wednesday morning (29th) Ryanair 09.35
Back from Athens into Gatwick on the Friday evening. Leaving Athens at 9.50pm
Staying in Monastiraki (will have to check name of Apartment)