For the central depot the RAF was forced to create a store: in 1938 it bought a quarry at Harpur Hill in Derbyshire; it built concrete storage structures within the quarry and then backfilled the hole with waste stone. Difficulties with construction and the weather prevented Harpur Hill from opening until mid-1940.
Harpur Hill had been designated the central store for such devices in April 1940, receiving its first load in June of that year of mustard gas bombs evacuated from France. In June 1942 it was decided to move the bombs to a remote site at Bowes Moor in County Durham.
The main storage site is now used as cold storage, however there are tunnels that link into the site that for the most part have been sealed, I walked for about half a mile down this tunnel and didn't find the end.
sorry for the limited number of pictures but the tunnels were all the same.
The floor is wet due to the constant leaks from the roof.
One of the joining tunnels that is sealed