Gwernllwynchwith Engine House is a ruined structure of possibly the earliest surviving rotary (as opposed to reciprocating) engine house in Britain, that was built between 1772 and 1782 to house a winding engine for the Gwernllwynchwith Colliery (NPRN 33490). The engine house was out of use by 1786. The ruin is of great importance to the history of technology, as it had previously been thought that no rotary steam engines were used before 1784 when by James Watt started to build engines for colliery winding.

Sources:
Site entry by Stephen Hughes for Buildings of Glamorgan, John Newman, 1995
Collieries of Wales, RCAHMW
A Guide to the Industrial Archaeology of the Swansea Region, by Stephen Hughes and Paul Reynolds, AIA, 1989

Claire Parry, RCAHMW, 24 August 2011