Former Lewis Merthyr Colliery Trefor winding engine house

The former Lewis Merthyr Colliery Trefor winding engine house is a Grade II* listed building. It features a south elevation made of snecked rockfaced sandstone with matching dressings, while the longer east and west elevations are constructed from rubble stone with rockfaced stone dressings. The north side is built of yellow and red brick, topped with a Welsh slate roof. This single-storey rectangular gabled structure has five bays on the sides and three on the gable ends.

The south elevation showcases tall pilasters flanking a central round-arched doorway, which contains six-panel double doors and a radially glazed fanlight. This doorway is flanked by two long windows with 38 panes, which have been renewed. Above the doorway are two inset tablets inscribed with "LMC" and "1890," along with quoins and a plinth. The side elevations feature round-headed windows with voussoirs, keystones, quoins, and sills, also with renewed multipane glazing. The east side has square vents with heavy lintels above the plinth, while the west side has round-headed arches.

The north elevation includes windows at two levels to provide a view of the head frame, along with a pair of winding cable slots at the center. The gable, which was originally partly timber, has been rebuilt in brick in the early 20th century, although the sides remain rockfaced stone. The roof is equipped with two tall square ventilators and has cast iron compressed air pipes fixed vertically at the north angles for steam exhaust. Additional compressed air pipes with valve control were added to the south gable in 1956.

Inside, the building has an open timber-framed roof, with yellow brick side pilasters and window dressings. The floor is made of quarry tiles and metal plates. The engine house contains a large conical winding drum powered by a complete engine from 1890, which features two horizontal, double-acting cylinders with a nameplate on the valves inscribed "Worsley Mesnes of Wigan."