Snowdonia's slate once roofed the world, employing thousands of workers across scores of mines in North Wales. But that was in its heyday, in Victorian times. Today, whilst the industry still exists, it employs just 350 people.

Helen Mark finds out what's become of the abandoned slate quarries and caverns today. Some are now places of leisure, with zip wires above ground, trampolines in underground slate caverns, and with scuba diving opportunities in flooded quarries, but others, as Helen discovers at Dorothea mine, are rapidly being reclaimed by nature.

Producer: Mark Smalley.