Due to being in an area of trees I have a few more clues just incase the GPS doesnt play, once in the correct area you shouldnt need acurate GPS readings. From the castle take the path to the right as sign posted passing two cottages leading to a lane. When you reach the Pumporth cottage take the left path passing the back of a garage. Following the path you will see the rear wall of the castle. Follow the path down and take the right path at the fork down the steps. You will arrive at a overgrown view point with two bench seats. The cache site is near.
Once you have grabbed the cache, why not visit the castle or continue down the path to the river. At the river turn right and follow upstream to the Coracle display. The road at this point leads back up to the Cilgerran main road.
** Congratulations to L60URA and Triibez for FTF **