What makes this window particularly striking is the disparity between its interior and exterior dimensions, a feature recorded in precise detail by Ordnance Survey correspondents in 1839: nearly two and a half metres wide on the inside, it narrows to just sixteen centimetres in breadth on the outer face. That kind of dramatic internal splaying was a deliberate architectural choice, designed to flood a dark interior with as much light as possible while presenting only a thin opening to the elements. That it survives at all, along with a second window at the eastern end of the south wall, is something of a small wonder.

The church is dedicated to St. Drenan, whose feast day falls on the 12th of December, according to Healy writing between 1874 and 1879. It stands on a steep slope on the southern side of a small valley in County Kilkenny, set within a roughly lozenge-shaped graveyard. The building itself is a rectangular undivided structure, meaning it has no chancel or internal division, measuring about 12.6 metres east to west and 7 metres north to south, built from roughly coursed rubble with mortar notable for its high pebble content. The western end has fared considerably worse than the east; the west gable survives to barely a metre in height, and the stretch of north wall near it, along with the area where the doorway once stood in the south wall, is gone entirely. By 1839, when Ordnance Survey officers documented it, the church was already missing about 4.5 metres of the northern side wall near the western gable, and the west gable itself carried a broken belfry. A graveslab associated with the site has been dated to the thirteenth or early fourteenth century, suggesting the graveyard was in active use during the medieval period.