You’ll be able to find wi-fi at most hotels, cafes, bars and restaurants throughout the well-touristed areas of Greece. Alternatively, you can pick up a local SIM card with a data package for continued access.
There are three main carriers in Greece: Vodafone, Wind and Cosmote. Their prices vary, as does their coverage, but Vodafone is probably the best for a traveller in Greece. A local SIM card with 12 GB data costs approximately EUR 25 and is valid for one month. There are cheaper options for those spending less time in the country.
To pick up a local SIM, just visit a Vodafone, Wind or Cosmote shop in Athens or in one of the tourist areas of whichever city or island you’re visiting. Top ups can be done in store, at supermarkets, or there may be street vendors offering recharges too.