Penrhos engine house dates from about 1794 and was built by John Wilkinson to house a beam engine for pumping water from a coal mine on the site. It is believed to be the earliest surviving colliery engine house in Wales. In the 1840s the building was converted into a cottage: three floor levels and associated window openings were been inserted above the basement, two domestic-type brick chimneys were added and remains of a pigsty are visible. The building is roofless, having walls of sandstone rubble with ashlar dressings to corners and window arches. In plan, it measures approximately 6.5m square and the bob wall, adjacent to the capped mine shaft on the south-east, is 1m thick.
B.A.Malaws, RCAHMW, 21 September 2010.