The dramatic ruins of Carreg Cennen Castle are perched on top of a 300ft limestone crag. Archaeological evidence shows that this naturally defensive site was in use at least as far back as the Roman period and probably earlier, but the first mention of a medieval castle is in 1248 when Rhys Fychan regained control after his mother had handed the castle over to the English out of hatred for her son.

Nothing remains of this earlier castle, the current buildings date back to the late 13th and early 14th centuries. In 1277 Edward I seized control of the castle, and in 1283 he gave it to one of his barons, John Giffard of Brimpsfield in Gloucestershire. It was probably during Giffard's tenure that the present castle was built.

The castle consists of a square inner ward surrounded by natural cliffs and rock-cut ditches. The more easily approached north and east sides are further protected by the walls of an outer ward, and the gatehouse is protected by an elaborate barbican that houses a long stone ramp with several deep pits that were covered by movable bridges. Steep steps descend from the south-east corner of the courtyard to a vaulted passage on the edge of the cliff that leads to a natural cave beneath the castle. Bring a torch or hire one from the farm if you want to explore this cave. Although water gathers in the cave it would not have been enough to supply the castle and the cave was probably walled up to prevent its use by assailants.

During the revolt by Owain Glyndwr at the start of the 15th century the castle was badly damaged. It was subsequently repaired, but its restoration was short lived. During the Wars of the Roses the castle was owned by the Duchy of Lancaster. Following the Yorkist victory at the battle of Mortimer's Cross in 1461, Carreg Cennen became a refuge for large numbers of Lancastrians. A Yorkist force was sent to force their surrender, and when the Lancastrians vacated the castle a team of 500 men moved in to demolish the fortress. The castle was never repaired and has been a ruin ever since.