That this one also sits inside a promontory fort, on a north-facing slope above the Wexford coastline, and was itself fortified, makes it something else entirely. Saint Catherine's Chapel at Nook is not quite what most people picture when they think of a medieval place of worship.

Built in the fifteenth century and dedicated to Saint Catherine, the chapel functioned as a chapel-of-ease, meaning it served outlying parishioners who could not easily reach the main church at Dunbrody. It almost certainly served a grange, which is an out-farm or agricultural estate, connected to the nearby Cistercian abbey at Dunbrody. What survives is a rectangular structure measuring just under thirteen metres east to west and a little over six metres north to south, and it survives remarkably well, with most of the north wall being the principal loss. The east and west walls are built with a base batter, a slight outward slope at the foot of the wall that adds structural stability, a detail that suggests the builders were thinking carefully about durability. The east window retains two lights with cusped ogee heads and tracery above, fitted with glazing grooves, which would once have held glass. When the antiquarian George Victor du Noyer recorded the chapel in the 1860s, he noted a small ogee-headed niche on the outer face of the north wall, set about one and a half metres from the ground, which he interpreted as a shelf for a lantern. That niche, and the pointed doorway beside it, are now gone.

The most architecturally interesting feature is inside the west wall. A lintelled doorway opens onto a mural staircase, a stairway built within the thickness of the wall itself, which leads both upward to what remains of a wall walk at the south-west corner and inward to a small gallery or chamber. That chamber has a fireplace set into the west wall, and its floor was once supported on stone corbels projecting from the north and south walls; one corbel survives at the west end of the north wall. Whether this upper space was a residential room for a resident priest or chaplain, or served some defensive purpose in keeping with the chapel's fortified character, is not recorded. There is no sign of a burial ground or enclosing wall associated with the structure, which sets it apart from most rural Irish church sites of comparable age.