Inside the tunnels of the Somme battlefield
4 October 2012 Last updated at 23:48 BST
A team of British and French archaeologists have entered a labyrinth of tunnels under the Somme Battlefield in northern France that have been untouched for almost 100 years.
The tunnels, 80 feet down, were dug so that troops could lay explosives below enemy lines.
Robert Hall has been given exclusive access.