Rick Edwards and Beau Ouimette head to north Wales to investigate waterways that may contain signs of the medieval Welsh Rebellion. Conwy Castle was constructed by Edward I between 1283-1287 after the Welsh Rebellion of 1282-3. The castle was part of a chain of fortifications known as the `Iron Ring of Castles" and was both a material and symbolic sign of English power and dominance. Edward I selected its site on a high rock perched above the estuary of the River Conwy so that the castle could be supplied by the river in times of siege. Day two finds the pair at Ruthin Castle, a medieval fortress overlooking the River Clwyd.