This small building to the west of St Columba’s Chapel at Kilneuair is described by the authorities as an oratory. Canmore has the following description:
Probably 18th century. A ‘folly’. Square. Rubble, employing ancient carved stones (probably from the chapel); roofless. Very curious small windows formed as acute triangles with slightly curved sides (New built up).
T S Muir “Characteristics of Old Church Architecture” 1861 p 82.
Muir accepts it as an authentic mediaeval oratory.
What I find interesting about the structure is that it appears to have been built around a well, or at least a deep hole which could have been a well. Like the chapel, it is in danger from the sycamores growing inside it.
Here are the “windows” in close-up for comparison: