Former Lewis Merthyr Colliery Trefor winding engine house

S elevation to Coedcae Road is of snecked rockfaced sandstone with matching dressings; long side (E and W) elevations of rubble stone with rockfaced stone dressings; yellow and red brick to N; Welsh slate roof. A single main storey rectangular gabled structure of 5 bays to sides and 3 to gable ends. S elevation has tall pilasters either side of a central round arched doorway with 6 panelled double doors and radially glazed fanlight flanked by 2 long 38 pane windows with renewed glazing; above are 2 inset tablets inscribed LMC and 1890; quoins and plinth. Side elevations have round headed windows with voussoirs, keystones, quoins and sill and renewed multipane glazing; square vents with heavy lintels above plinth to E and round headed arches to W. N elevation has windows at 2 levels to give a view of the head frame and a pair of winding cable slots at the centre; gable formerly partly of timber with different fenestration but rebuilt in brick early C20 though rockfaced stone at sides; roof has 2 tall square ventilators, cast iron compressed air pipes fixed vertically at N angles for exhaust of steam; fixed to S gable are compressed air pipes with valve control added in 1956. Lower level N has central round arched doorway and remains of arches on W side with rockfaced stone bases of headframe supports attached at corners.

Open to timber framed roof inside; yellow brick side pilasters and dressings to windows; quarry tiled and metal plate floor. Houses a large conical winding drum powered by a complete engine of 1890 consisting of 2 horizontal, double-acting cylinders with nameplate on valves inscribed Worsley Mesnes of Wigan.