At the northernmost part of the island, 11 kilometres off the modern town, under the medieval town of Skiathos, there is a beached named Kastro in honour of the natural fortress above it. With crystal clear waters and an imposing natural landscape, the beach is exposed to the wind, so it usually has waves. It is not an organised beach but it does have a taverna. After swimming in its impressive waters, one should visit the ruins of the ancient town and admire the view from above.

Kastro can be reached very easily on any of the boats that daily depart the port of Skiathos. If you decide to access it by car, you should know that the road stops before Kastro and the rest of the distance must be done on foot.