Greece's monetary unit is the Euro. No other currency is accepted and it is best to exchange dollars or other currency at a bank. The exchange rates are all the same throughout the country and you exchange money at a bank or official exchange shop where you will get the best running rates. Currency exchange shops and banks in very touristy areas charge high commissions, so make sure you know what the commissions are before you commit to a transaction. Banks are open from 9:00 AM until 2:00 PM. At the new airport near the luggage pickup you can find machines that can exchange foreign currency and return Euro. Very nice indeed since you need the Euro for a luggage cart.