Plot: Hidden beneath the hulking great Pennines, Julia sets off from the ancient village of Dufton in search of one of Britain’s best kept secrets – the Grand Canyon of the North, a magnificent hanging glaciated valley, that’s been 500 million years in the making. A true highlight of the Pennine Way, it was described by walking legend, Alfred Wainwright, as a ‘natural wonder’ and ‘unforgettable sight’