House sitting job over and we have a week until we are expected in Spain for a helpx job.
So..... East we go. More or less following the front line from WW1 across France.
First stop Arras.
The Battle of Arras was a British offensive during the First World War. From 9 April to 16 May 1917, British, Canadian, New Zealand, Newfoundland, and Australian troops attacked German defences near the French city of Arras on the Western Front.

The memorial dedicated to the NZ tunnelers.
The Arras region is chalky and was easily excavated; under Arras itself is a vast network of caverns and underground quarries. They devised a plan to add new tunnels to this network so that troops could arrive at the battlefield in secrecy and in safety. The scale of this undertaking was enormous: in one sector alone four Tunnel Companies (of 500 men each) worked around the clock in 18-hour shifts for two months. Eventually, they constructed 20 kilometres of tunnels, graded as subways (foot traffic only); tramways (with rails for hand-drawn trolleys, for taking ammunition to the line and bringing casualties back from it); and railways (a light railway system).
The bulk of the work was done by New Zealanders. We visited the Carriere Museum and went down into one of the tunnels that is open to the public. Some are named after towns and cities from New Zealand. The one that was part of the tour was the Wellington Tunnel.

Just before the assault the tunnel system had grown big enough to conceal 24,000 men, with electric lighting provided by its own small powerhouse, as well as kitchens, latrines, and a medical centre with a fully equipped operating theatre.

Thousands of soldiers were billeted in the tunnels for eight days prior to the start of the Arras offensive on 9 April 1917. At 05:30 that morning, exits were dynamited to enable the troops to storm the German trenches. The Germans were taken by surprise and were pushed back 11 km. This counted as an extraordinary success by the standards of the time. However, the offensive soon bogged down and it was eventually called off after casualties reached 4,000 a day.
As you could imagine it was a very sobering place. The guides that were there the day we toured we're very interested that we came from New Zealand as they had just had several dignitaries from NZ there for the wreath laying ceremony commemorating the end of World War 1.

During World War II, the tunnels were re-opened to serve as air raid shelters. They were sealed again in 1945 and were largely forgotten until their rediscovery in 1990.