Dinefwr Castle (sometimes anglicized as Dynevor) is a Welsh castle overlooking the River Tywi near the town of Llandeilo, Carmarthenshire, Wales. It lies on a ridge on the northern bank of the Tywi, with a steep drop of several hundred feet to the river. Dinefwr was the chief seat of the Principality of Deheubarth. The castle is in the care of Cadw but lies within Dinefwr Park, which is owned by the National Trust. Visitors who wish to see the castle and are driving there, may pay admission for the car park, if not National Trust members. A separate fee is payable if you wish to visit Newton House. Alternatively, access is free to walkers from Llandeilo town nearby, and there is a small free car park near the castle, but it can only be reached by a rough track through the deer park.