The castles of Gwynedd are about as picturesque as it gets, but few tick as many classic boxes as this gorgeous wonder on the Irish Sea. Harlech Castle stands on top of a spur of rock by the sea, a stunning location for a beautiful piece of work, one of the most impressive examples of late 13th and early 14th century military architecture in Europe (UNESCO’s words, not ours). It is hard to imagine a more awe-inspiring setting for a castle. The castle lies in the town after which it is named and is easily accessible via train, bus or bike.