Big Pit was originally an iron mine, driven into the side of the mountain not far from the surface due to the shallow iron deposits, the level is called Engine Pit Level and can still be seen on the bridge connecting Blaenavon and Garn Rd at 51.773998, -3.092075 coordinates. The Iron Workings are above the Big Pit coal workings, for some time Engine Pit Level was used as an emergency exit for Big Pit whilst it was working, now the River Arch Level is the escape route. Engine Pit Level was driven around 1810 by hand due to dynamite being invented 5 decades later. There are a few pictures online showing the interior of the Engine Level from the 60’s when miners from Big Pit explored the level, finding an old flange-less wheel’ed dram inside, now at a museum.
