The creation of man-made underground tunnels played a huge role in the outcome of the First World War. They were first dug to mine under enemy positions and detonate bombs or attack in desperate and fierce fights. As the war dragged on, nevertheless, they developed another purpose: providing soldiers with safer accommodation and communication routes. In this episode of Snow on the Road, Dan visits the tunnels of the Vimy Ridge built by Canadian miners and the Carrière Wellington tunnels, now a museum in Arras, France.