Inside that boundary stand the remnants of the medieval parish church of Errigal Trough, two gable walls and not much else, yet the site carries an unusual density of things that have been moved, lost, or quietly closed off. Carved corbel heads were taken to Favor Royal in County Tyrone. A graveslab commemorating Prior Tullius Kena, noted by the scholar John O'Donovan when he visited in 1835, has since vanished entirely. And there is an unconfirmed record of a sheela-na-gig, one of the enigmatic carved figures of a female form found on medieval Irish ecclesiastical buildings, that was removed to the Ulster Museum, though this identification remains uncertain.

The church was dedicated to St Meallán, an associate of St Fursa, a seventh-century saint from County Down. Meallán is otherwise obscure; his feast day falls on 26 October, and beyond that, very little survives of his story. Clergy attached to the church are documented from 1441, and by the time of Spottiswold's Visitation in 1622 the building was already described as ruinous. It was subsequently rebuilt and served Protestant worship until 1824, when a new Church of Ireland church was opened roughly 150 metres to the south-east. What remains today is the west gable, just over eight metres long, with a central doorway whose round arch is a later reconstruction, and the east gable, slightly shorter, with a wide pointed opening from which the dressed stones have been robbed. The graveyard's headstones date almost exclusively to the eighteenth century, with the McKenna name appearing repeatedly across them.

Across the road to the north-east, St Meallán's holy well sits at the base of a north-east-facing rock face, its water collecting in a small D-shaped recess before overflowing across a stone platform to the stream below. Holy wells in Ireland were traditionally the focus of patterns, communal gatherings combining religious observance with socialising, often held on a saint's feast day or a proximate date. Here, folk memory records a two-day pattern held around 30 August each year, until the well was closed in 1836. There is no evidence of active veneration now, though the well itself, accessed by a short path down from the road, remains findable.