My favourite town in Greece is Kastoria. See here why.
Although I prefer the sea to the mountains, my grandfather's village, Iliochori (Hλιοχώρι), is always an oasis. It is a small village in the Ioannina area, shortly after Tsepelovo. There you can find a spectacular double waterfall and a plane-tree whose perimeter is over 10 m. It also offers a very dark sky for observing the southern and eastern night sky.