In this final episode Will gains exclusive access to explore the usually inaccessible locations that are home to some of the biggest engineering projects in Wales, both past and present.

Will explores the hidden pieces of history from World War Two. Wales made a huge contribution to the war effort and the remote countryside was witness to many military activities.

Will travels to North Wales to discover the forgotten history of the slate industry. Welsh slate once roofed the buildings of the British Empire and the industrial revolution.

Wales once led the world in the production of coal, exporting the black gold to the four corners of the Earth. Since that industry collapsed, much of the infrastructure has been destroyed, forgotten or hidden away.

Will discovers the forgotten story of how Wales once led the world in copper production by visiting some extraordinary and abandoned locations.

Will explores some Wales’s most intriguing and hard-to-access caves.