Matt Baker heads to Snowdonia National Park, where he hitches a ride on a train that relies on the laws of gravity to move it, and finds out about the challenges of farming on the side of the highest mountain in Wales. Joining him is Ellie Harrison, who meets the man who's come up with a novel way of growing mushrooms and discovers what is being done to control the foreign invaders threatening our native wildlife. John Craven is in the Orkney Islands in Scotland to investigate controversial plans to harness energy from the sea, while Adam Henson's got some expert advice for Kate Humble as she gets to grips with pig production on her smallholding in Wales.