Helen Mark is in Dorset to investigate the county's ancient sunken roads, known as holloways. They're deep, steep-sided tracks formed when soft rock erodes and are often overtopped by a canopy of trees. The erosion over centuries creates remarkable, often otherworldly spaces, that come with their own unique flora and fauna. On her trip to the Symondsbury estate near Bridport Helen hears about how the cave spider and goblin's gold moss can thrive in the cracks of these unlikely rockfaces. She is joined by Andy Jefferies and Rosie Cummings from Natural England who are behind a project to map Britain's extensive network of holloways. The holloways often come with their own folklore too. Local storyteller Martin Maudsley recounts the legend of the Dorset colpexie - mischievous sprites that can taunt the unwary traveller! Producer: Robin Markwell Presenter: Helen Mark