Chapel of St. Deniol was probably erected in the 12th century in the area of a small monastery dating back to the beginning of the 6th century. After the disappearance of the Celtic monastery, this place was taken by a group of nuns from Aconbury in Herefordshire. The monastery was dissolved by Henry VIII in 1534, its buildings became the residence of clergy of the local parish church, and the chapel with time fell into disrepair.
The chapel was a simple, small, aisleless building on a rectangular plan, covered with a gable roof mounted on two triangular gables of the shorter sides of the building. Its lighting was provided by medium-sized pointed windows. There was a small crypt inside.
The chapel was rebuilt in the early modern period into a fernery, among others some of its windows were transformed. Currently, it is an unroofed ruin.
Website wikipedia.org, Penally Abbey.