A couple of days in Athens, then 2+ weeks on Crete. Visit Minoan sites like Knossos and Phaestos, major museum in Heraklion, and Matala for the beach and history. Also some time in city centers Rethymno and possibly Chania and eastern island. Amari Valley, WWII historical sites briefly, some hiking and lots of culture soaking... including some Greek language study. Maybe a couple of bike rides, possibly hire a car for a few days. Buses get you close to the populace, a a taxi ride on the last trip made for outstanding experience.
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