There are ATM machines in many locations, most of which will dispense local currency (euros). They do, however charge fees.  Greeks, in general, do not use credit cards and most of their transactions are done in cash (including rent and utilities). 

We are currently working on a smoother system of setting up a U.S. Dollar account and a Euro account at a local bank. This will allow money to be transferred (electronically wired) from an account in the US to Greece. This money can also be transferred to the Euro account, which comes with a local ATM card.

Credit cards are taken at all the major stores and restaurants.