A detail from an 18th Century map showing Pen-y-Castell hill fort.
Sites in Pen-y-Castell
Images
Articles
This photo clearly shows the hillfort, and to the east of the fort (about 3.5cm) is the standing stone, discernable as a small pale white dot. The stone is nearer the field boundary (marked by a white track) than the fort itself.
Yet another link for the ADAS – but their site is very useful for this part of the country so I make no apology.
This webpage shows the older standing stone in front of the hillfort.