New “Eleftherios Venizelos Athens International Airport” has earned a great number of international awards, as one of the best airports in the world.
There are many things to do, like shopping, eating, relaxing, plane-spotting, internet surfing, even praying in the church. Over 50 selected shops and 14 dining facilities with a wide variety of specialties operate in the Shopping Centre of Athens International Airport. There is also a permanent exhibition dedicated to Eleftherios Venizelos and the excelant Airport Archeological Museum. The airport also hosts cultural events, including painting and photography exhibitions, book presentations etc. The Airport's Retail Park is very close to the airport. You can spent a lot of time there, visiting 4 superstores: IKEA, Dixons, Leroy Merlin and Factory Outlet (a discount clothes and footwear superstore).
If you want to take a nap or a shower, there is also a 5 star Sofitel Hotel, but it’s expensive. See more info about the hotel here: http://www.sofitelathens.gr/en/
The airport provides dedicated storage space where travellers can safely leave their luggage. Look here for their price list: http://188.8.131.52/UserFiles/File/travelers/services/baggage/150709_pacific_pricelist.pdf
There are buses, metro, suburban railway and taxis, connecting airport with Athens center. All of them is running 24 hours. My suggestion is to take the metro and be in Athens in 30 minutes. A return ticket will cost you 10 euros. Syntagma station is the city center, Acropolis station is very convenience for visiting this unique monument and Monastiraki station is very close to Plaka area.
If you want to travel to Vonitsa with a bus, take the X93 express bus from Airport (arrivals level) to the Kifissos Coach Station (KTEL). You will be in the bus station in 45 minutes and the ticket costs 3,20 euros. There are many daily departures from there to Vonitsa and the trip’s duration is 5 hours. You will also have the opportunity to cross the new fantastic Rio-Antirio Bridge.Hope that helps, but feel free to ask anything you may need. You can also click on Athens International Airport web page here: www.aia.gr for more info. I wish you the best for your visit in Greece.