In the middle of winter, the team arrives at the Ffestiniog Railway in Snowdonia to find out how millions of tons of slate were moved down the mountain. This is the slate that covers roofs in every corner of the country, and all of it was moved by rail.
Underground, Alex experiences the brutal conditions faced by miners in Llechwedd quarry who would have endured 12-hour shifts suspended from iron chains. It's an exhilarating ride down the narrow winding track aboard the 'gravity train' with the whole crew hanging on to the brakes all the way.
At Foxfields Railway in Staffordshire, built to transport coal to the nearby mainline, Ruth gets on the loco's footplate as it is driven up the steepest railway in Britain. Coal was to change everything in our day-to-day lives, right down to the way we cooked, the shape of our pots and the role of women who had to deal with the tyranny of keeping clothes clean in this dirty industrial world.