WW1 Practice Tunnels/Trenches Found Under Salisbury Plain

It's trenches and tunnels, not that it's immediately obvious from the text.
"A "unique" network of tunnels used to train soldiers to fight in World War One has been found on Salisbury Plain.
Archaeologists working with the Ministry of Defence, which is building hundreds of military homes at Larkhill, made the discovery.
The site was used to emulate conditions soldiers would face in trenches in France and Belgium during the war.
More than 100 pieces of graffiti have been uncovered in the chalk walls of the trenches and tunnels.
Soldiers training on the site who left their names include decorated heroes and one recorded deserter."
WWI practice tunnels found under Salisbury Plain - BBC News