Not really rail related, but Cornwall and Devon have miles and miles of abandoned tunnels. Many of them were dug several centuries back, some possibly even as long ago as Roman times. They were originally tin or lead mines but after abandonment were in some cases used or even extended for smuggling.. Jamaica Rum or spices on which the government at the time levied heavy duties would be clandestinely offloaded from sailing ships and hidden away in tunnels before presumably being sold on the black market.. Many coastal communities lived almost entirely off such illegal activities in what was otherwise a very poor part of the country. Daphne Du Maurier's excellent novel Jamaica Inn is set in this period and accurately portrays some of the consequences.