TicketsFares for Blue Buses and Trolleys: 50 euro cent, children under 6 travel free, tickets are available at many public periptera or kiosks where you'd buy magazines and sundries.
As well as the special kiosks that only sell tickets near the bus stops (often/usually/almost always; closed except am hours).
Term of Validity: Only for a single
journey.
Validate the ticket only once at beginning of your first trip.
Validation: When boarding have
your ticket in hand and validated through the validating machine on board or outside or where ever they placed them - the metro uses the same machine almost. You put 
your ticket in
the bottom slot and the machine stamps it after a second then you take it and put it somewhere handy until leaving the premises.
The penalty for not having validated your ticket is 40 times the purchase price or 18 euros. Tickets are valid for one trip only.
24-HOUR TICKET: Ticket price:
3 Euros
Validity: Allows unlimited travel by all public transport modes (buses,
trolley buses, metro) and ONLY ONE trip
to or from the Athens International Airport "Eleftherious Venizelous".
Where to buy Tickets: All tickets including the 24-hour can be purchased from the drivers of
the airport buses, all metro stations and public transport outlets.
NOTICE: Children under the age of six travel free
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