Jet has become so inextricably linked with the sea cliffs around Whitby, that many people are unaware it was extensively mined throughout the North York Moors and Cleveland Hills. Since 2014, members of the North York Moors Caving Club have been involved in a project to explore these long-forgotten workings, for which few contemporary records exist. Previously regarded as a cottage industry with trivial underground working, we have since re-discovered a period of frantic mining activity driven by fashion and mapped jet workings measuring over 12km in length on a single site alone.