It enters from the northwest, exits to the southeast, and in doing so passes clean through what was once the main working floor of a two-storey rectangular mill. The arched opening that once carried it through the southeast wall is now blocked, but the shallow earth-cut channel survives, along with foundation stones at the northeast end of the building where machinery once stood. It is the kind of detail that makes a ruin readable, the invisible logic of water and work still legible in the ground.

By 1837, the writer Samuel Lewis was describing the site as an extensive operation combining a bleach-green, flax and tucking mills, and wool-carding and spinning machinery. A tucking mill, also called a fulling mill, used water-powered hammers to pound and clean woven cloth, consolidating the fibres. Lewis named the proprietors as Messrs. J. and F. Atkins, who had recently added a power-loom for blanket manufacture. The 1842 Ordnance Survey six-inch map labels the complex a Bleach Mill and Woollen Factory and shows the full extent of the operation: a millstream drawn from the Funshion almost two kilometres to the northeast, a large field designated as a bleach green where cloth was laid out in the open air to whiten, and a watch house, now vanished, presumably for supervising the drying cloth. The bleach green field, measuring roughly 230 metres by 110 metres, is still identifiable on the ground. By the time the 1936 Ordnance Survey map was produced, the complex had been renamed Ballyderrif House, suggesting the industrial function had by then given way to residential use. The main mill structure is built in rubble limestone with ashlar quoins, the cut corner-stones that give structural and visual definition to a rubble wall, and three substantial additions project from its southeast elevation, each with its own roofline, chimney, and blocked or altered openings. A mid-to-late nineteenth-century house to the southwest of the mill, with its brick-surround windows and central porch, likely housed the mill's management or owners at the height of the complex's operation.