Countryfile - Underground Britain: Sean Fletcher is in Cornwall, but he’s not here to explore its fabulous 300-mile coastline. Instead, he goes underground to unearth the legacy of the county’s renowned tin and copper mining industries. Sean encounters an endangered mammal that has set up home in disused mine shafts at Prideaux Wood, and at Penwith we delve underground to discover the history and geology of a 500-year-old tin mine that contains some of the deepest seams in the country.