The visible land here in the Fforest Fawr Geopark has been worn down by glaciers into rolling mountains cut through by river valleys. Looking more closely on winding walks through the quiet you come across holes into the stony grassland that lead into vast cave net-works where water and wind travel through what Robert Mcfarlaine so vividly described in his extraordinary book as the 'Underland'. The Call Series has been growing since I read 'Underland'. The Call XIII shows the surface world and the underland and how the two feel very alive.