Perched dramatically on the island's rocky northernmost headland, 9km north of Skiathos Town, Kastro was the fortified pirate-proof capital from 1540 until it was abandoned in 1829. At its peak it held 20 churches and 500 homes; now, among the restored ruins, you'll find an old cannon, a Turkish-era mosque, several water tanks and four churches (including 17th-century Christos, home to several fine frescoes). Drive or walk down the steep sealed track, or join a boat trip from Skiathos Town.
Kastro passed through Byzantine, Venetian and Turkish hands before being deserted in favour of its modern counterpart. The area is a spring mecca for birdwatchers, who may spot long-necked Mediterranean shags or blue rock-thrushes skimming the waves, and there's a small pebble beach below.
