Dinefwr Castle (Welsh: Castell Dinefwr; also known as Old Dynevor Castle) is a ruined castle overlooking the River Towy near the town of Llandeilo, Carmarthenshire, Wales. It lies on a ridge on the northern bank of the Towy, with a steep drop of one hundred feet to the river. Dinefwr was the chief seat of the Dinefwr dynasty of the Kingdom of Deheubarth. The castle is a Grade I listed building.[1]