Inside Somme tunnels left untouched for 100 years
5 October 2012 Last updated at 14:21 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 are the deepest that have been discovered in the area and were dug so that troops could lay explosives below enemy lines.
The BBC's Robert Hall has been given exclusive access to them and is in the village of La Boisselle.