Little has survived of Skiathos island's past and much of what hasn't been lost over time and through neglect has simply been botched by cement mixers. Places that are worth a visit on Skiathos include the Kastro - a fortified former capital built in the 14th century on a rock outcrop above the main town. Skiathos Kastro was built as a refuge from marauding pirates, notably the Barbarossa brothers, and commands a dramatic position over the sea. the Kastro used to house more than 20 churches and 300 odd homes.
Only two churches have survived the ravages of time and the several half-hearted attempts at restoration. Also remaining are part of the wall and gate of the old fort as well as a half-ruined mosque and a cannon. A wooden drawbridge has been replaced by a flight of cement steps and a house has been rebuilt.
You can get to the Kastro on foot but it is a good three-hour walk. Most take one of the excursion boats that make the trip daily from Skiathos town and drop passengers at the bottom of a long series of steps up the cliff. There is a flat beach here of shingle and stone and a ramshackle beach taverna that gets packed out as the boats arrive. Nearby, and accessible only by boat, are three sea grottos, named Galazia (Blue), Skotini (Dark) and Chalkini (Copper).