A trip through Wales' highest peaks and deepest valleys. Starting in Pwllheli in the north west, the route heads along the lines that were built during the slate industry's heyday. At Porthmadog, the journey briefly switches to the reconstructed steam trains of the Welsh Highland National Heritage Railway to Minffordd station. Nearby is the village of Portmeirion, famous for its role in the classic TV series The Prisoner. Rejoining the Cambrian Line, local farmers reveal what the railway means to them, before the route takes in the seaside resort of Aberdovey.