In August, the mornings will be your best bet for sightseeing, as the heat grows strongest about 1pm, making the Greek habit of taking an afternoon nap or relaxation period very attractive.
Many Greeks travel home for the Festival of the Assumption of the Virgin Mary, also known as the Dormition, on August 15th, which is celebrated throughout Greece. It's a national holiday, so many sites and businesses will be closed.
Because of the increased domestic travel, transportation is usually jammed. Travelers with Greek surnames reportedly seem to fare better on getting that last seat during the first two weeks of the month. Travel on and around the 15th itself is subject to limited schedules or fully-booked ferries.
Many Greeks will also be observing a Lenten-like fast for the period between August 1st and the 15th, when the fast gives way to feasting. This generally does not affect what is available for tourists to eat, though some additional fast-friendly specialty dishes may be worth a try.
The cultural festivals of Greece are in full swing as the Patras Festival begins, and dozens of other major and minor festivals take advantage of the crowds to present the best of Greek culture to as many minds and souls as possible. The island of Aigina offers its classically-flavored International Music Festival.
Grape harvest festivals are underway in several places. The Dodecanese islands of Samos and Rhodes both host major festivals.
Traveling during the Full Moon? Check to see if any local site is open for the annual Full Moon in August festivities. The choice of sites changes each year. If there are two full moons - a "blue" moon which occurs more often than we think - the Full Moon in August will be held on the second full moon.
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