Clara,
If this the place you are going to stay (www.halkidiki.com/fani/), you'll be staying in the center of Vourvourou. Everything is very close (walking distance).
As for the sea, the water is already warm enough.
Watch the weather on this page: www.halkidiki.com/english/weather_e.htm
Weather station is set up just 1 km away from Fani Apartments.
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Nikos
Forum Admin
nikos at halkidiki.com