In the Ionian Islands, the snorkeling off the island of Kefalonia is considered some of the best in Europe. There are plenty of shipwrecks and walls to explore.
To reach the snorkeling in the Greek Islands by air, start by using the international airline flights into Athens International Airport (ATH). From Athens, there are two major Greek inter island airline carriers and a handful of smaller airlines to consider (such as Sky Express). Most of the islands have at least small airports. While there are many ferry lines that interconnect the islands (such as Bluster ferries), the schedules can sometimes vary greatly with delays; therefore, the inter island flights might be the best option if you are on a tight schedule. Should you plan to take a ferry, make sure to advance-book a fast catamaran and/or hydrofoil ferry. The busiest times of year are from July through September where the number of visitors greatly out number the available air seats and accommodations, so plan accordingly.
Overall, Kefalonia is the 3rd most popular snorkel dive spot of all 18 snorkeling dives in Greece.