If you wish to let your property, you must register with the Greek Tourist Organisation, declare the income you make, and pay income tax in Greece. We can help with obtaining your registration papers.
Tax laws have been changing recently. There is a property tax to be paid every year, but it is not (yet) a lot of money. Your accountant will be able to give you the latest information.
If you own property here, but have never made a tax declaration that you own property in Greece, YOU MUST do so now.