Chris heads to the Alps to ride on six pioneering mountain railways. It’s the middle of winter, with snow and ice constantly threatening to derail his journey, as he crosses Austria and Switzerland on ever higher and higher railways to find out how and why these extraordinary lines were built. Along the way he faces some terrifying 19th Century winter sports and a climb up the North Face of the Eiger. Will Chris conquer the Alps? Or will they conquer him?

• Chris Tarrant