Edward I began Caernarfon Castle in 1283 as the centrepiece of his ring of fortresses meant to lock Wales into the English crown. Unlike the round, white-rendered towers of Edward's other Welsh castles, Caernarfon's are polygonal and faced with bands of darker stone — a deliberate echo of the walls of Constantinople, intended to wrap the new English regime in the legitimacy of Rome.
The result is one of the most theatrically impressive medieval buildings in Britain. The Eagle Tower at the western end is the showpiece; the King's Gate, never quite finished, was designed as a sequence of five doors and six portcullises that an attacker would have to break through one at a time. Inside, the great hall is a roofless shell, but several towers contain small museums — including the Royal Welch Fusiliers museum — and the wall-walks give long views over the Menai Strait, Anglesey, and the slate quarries inland. Allow at least two hours.