Felicity Evans visits the waterfalls and swallow holes at the western end of the Brecon Beacons, and discovers that besides its natural beauty, it's an area with a rich industrial heritage. Today its deep, mossy ravines are of great interest to walkers and potholers. But the waterfalls, Felicity discovers, gave rise to local industries - including a gunpowder works, and the silica mines provided firebricks that were shipped around the world.

She even walks behind one of the waterfalls, Sgwd Y Eira, the waterfall of snow.

Producer: Mark Smalley.