Former Lewis Merthyr Colliery Bertie winding engine house

S elevation is of snecked rockfaced sandstone, long side elevations E and W of rubble sandstone with rockfaced stone dressings and red brick N; Welsh slate roof. A single main storey rectangular gabled building of 5 bays to side and 3 to gable ends. S elevation has tall pilasters either side of central round arched doorway with 6 panelled double door and radially glazed fanlight flanked by 2 long multipane windows with renewed glazing; quoins and plinth. Side E and W elevations have round arched windows with renewed multipane glazing with rockfaced voussoirs, keystone, quoins and sill. N gable has 4 round headed windows to give view of headframe and a pair of winding cable slots at centre and was formerly of timber with different pattern of fenestration but partly rebuilt in brick early C20, though rockfaced stone to sides; stone bases of headframe supports attached at corners. Roof has 2 ventilators.

Open to timber framed roof; brick pilasters to side together with rest of interior painted black. Electric motor powering the large winding drum occupies N floor area, the rest used for audio visual presentations.