A complex series of mines was dug under the Ruined Castle in the early 1900s. The mines were a rich source of oil-shale.
The oil shale was transported from the mines along horse-drawn tramways, initially to the Aerial Cableway, and, after its collapse, all the way back to Katoomba.
Collapsed mine adits, the tramway benches and the mullock heaps can still be seen today.
Keen observers might be lucky enough to see the occasional relics - broken glass, part of a skip, a length of tramway track or the like.
Nellys Glen (Ford)
Blue Mountains National Park (NSW)