I love windsurfing and the only beach proper to practise it on Syros is Galissas. Of course, it gets very popular but if you go early in the morning or late in the evening, it is less crowded and you will not fear to harm someone while on your board. The sea is warm and clean and afetr bath, you can sit at the taverns and enjoy your meal. Not far from Ermoupolis and easy to go. The road there is OK but you have to leave the car at a parking area and then walk a little to the beach.