The nave, chancel, and walls are gone; what remains is the western end of a building that was deliberately reduced to a fragment in 1889, leaving behind a structure that reads less like a ruin than like an architectural afterthought, a punctuation mark with nothing left to punctuate.

The church that once surrounded this tower was dedicated to St. Nathlash, a figure whose name also attached to a much older place of worship on or near the same ground. The 1812 building replaced, or was built directly upon, that earlier medieval parish church of St. Nathlash. Interior fittings for the new church were provided by Richard Aldworth, a local landowner of some consequence in north Cork. The 1842 Ordnance Survey six-inch map marks the site simply as "Church", its position confirmed by a trigonometrical station. By 1889, however, the Church of Ireland parish had been unified with the neighbouring parish of Farahy, and the Rockmills building was no longer needed. Rather than maintain the full structure, the congregation took down the body of the church and left only the tower standing. It is a practical decision that now looks almost surreal.

What survives is carefully composed in its own right. The tower rises three storeys, with string courses, shallow horizontal bands of stone, marking each floor on the exterior walls. A parapet runs along the top before the spire begins, which is octagonal and limestone. On the south face, a round-headed entrance door is flanked by a matching round-headed window, with a D-shaped niche set into the wall above them. Inside, a small niche cut into the north wall once housed a heating stove, a modest domestic detail preserved in a space that is no longer quite a building at all.