This is a journey into the concealed geographies of the ground beneath our feet - the hidden regions beneath the visible surfaces of the world. From the vast below-ground mycelial networks by which trees communicate, to the ice-blue depths of glacial moulins, and from North Yorkshire to the Lofoten Islands, Robert Macfarlane traces an uncharted, deep-time voyage. From the prize-winning author of "Landmarks", "The Lost Words" and "The Old Ways".