May and early June, as well as September are the best times to visit Crete. The summer months are also a good time, but you will be competing with another 2 million tourists. The Meltemi (Northen winds) pick up between mid-june and the end of August and can become very uncomfortable, but they do provide some relief from the summer heat. At this time the waves make swimming a little more challenging.
The trip form Piraeus to Heraklion takes about eight hours and most ferries leave around 9:00 PM, and arrive in Crete around 6:00 AM. Booking a cabin for the overnight trip is a good idea, although many passengers rough it out on deck or on any comfortable spot they can find inside the bars and hallways. In fact many groups of travelers who do not have a cabin embark early and set camp in the most comfortable corner of the boat they can find. After 11:00 PM the halls are lined with sleeping passengers.
Also see: Ferries in GreeceDaily ferry boats from Piraeus to Heraklion:
Daily ferry boats from Piraeus to Chania:
ANEK Lines: C/F Lato, C/V LIssos
Daily ferry boats from Piraeus to Rethimno:
ANEK Lines: C/F Arkadi, C/F Preveli
Twice a week to multiple ports of Crete and other
C/F Vitsentzos Kornaros leaves for Crete twice per week and it is one of the older-type ferries that makes calls in ports not visited by the major ferry companies.
Boat service to and from the Cyclades:
C/M JetOne of AegeanJet sails connects several islands of the central Cyclades with Heraklion. It passes through (although not in the same trip) Sifnos, Milos, Ios, Santorini
C/M Flying Cat 4 of Hellas Flying Dolphins sails between Mykonos, Paros, Naxos, Santorini, and Heraklion.
Many boats offer connections from Santorini to Heraklion (daily), Rethimno, and Chania. In general they are smaller boats and the tickets between islands are expensive.
The main airport of Heraklion (Nikos Kazantzakis airport) serves most of the international and domestic flights, while Chania also has a smaller international airport. The small airport of Sitia serves domestic flights.
There are daily flights from Athens and less frequent ones from Thesaloniki. Many charter flights from abroad touch down on the island, and there is air service to and from Rhodos, Mykonos, and Santorini.