Criccieth Castle stands on a headland above the seaside town of Criccieth. Although the walls and towers of the castle are mostly in ruins the imposing gatehouse still helps the castle look impressive when seen from a distance. The spectacular views from the castle over the surrounding coastline emphasise the strategic position it had. The natural defences of sea and cliffs were supported by earthworks on the landward side.

Criccieth Castle was built for Llywelyn the Great in the 1230's. It is a long triangular enclosure separated into three courtyards by an inner ward. Due to the ruined state of the building and a lack of historical records detailing the construction work carried out at the castle, there is much debate about who built what parts and when. The massive twin towered gatehouse, although unique among Llywelyn's castles, is made up of two typically Welsh D-shaped towers, and is contemporary with similar gatehouses built at Montgomery and Beeston. An outer ward, protected by a new wall and three rectangular towers, was probably added by Llywelyn ap Gruffud (Llywelyn the Last), sometime between 1255-82.

In 1283 the castle was captured by Edward I. During his reign and that of his son, money was spent improving the castle. It is this work that is most difficult to identify, but it seems likely that the walls, towers and gatehouse were heightened.

In 1294 Madog ap Llywelyn led a Welsh revolt against the English. Criccieth Castle was besieged, but its coastal location meant it could receive supplies by sea and it was able to survive the siege. It was not so successful in 1403-4 when it was besieged during another Welsh uprising led by Owain Glyndwr. This time a French fleet prevented provisions and reinforcements arriving by sea and the garrison were forced to surrender. The castle was destroyed and the ruins were never rebuilt.