Kastro is a fortified medieval town perched on a rocky promontory at the northern tip of Skiathos. From the mid-14th century until 1829 it was the island's only settlement — the entire population lived here, protected by the sea on three sides and a drawbridge on the fourth. When pirates ceased to be a threat after Greek independence, the inhabitants dismantled their homes stone by stone and built the present town. What remains is extraordinary: crumbling walls, three surviving churches, and panoramic views across the channel toward Pelion.
You can reach Kastro on foot via a trail through the pine forest (about 8km from town, roughly two hours each way), or more easily by excursion boat from Skiathos harbour. Boats typically combine Kastro with a stop at Lalaria beach and a circuit of the sea caves on the north coast.