For four years, a disused slate quarry in a remote mountain in North Wales became home to some of the world’s greatest artistic masterpieces. In specially constructed air-conditioned underground chambers the priceless treasures in the collection of London’s National Gallery sat out the days of the Second World War safe from Luftwaffe bombers and Nazi art hunters.

The abandoned slate quarry was located beneath a small mountain named Manod Mawr, near the historic mining town of Blaenau Ffestiniog. The local slate mines have been driving the economy of this region since the 18th century. The 1860s and 1870s were the best years for the slate industry and Blaenau Ffestiniog underwent a large boom. But an economic recession followed by the First World War and the general trend towards mass-produced tiles and cheaper slate from Spain caused the industry to falter, and many quarries closed down.

Manod Mawr near Ffestiniog. Photo credit: Jeff Buck/Wikimedia

In 1939 war broke out in Europe and for a while things looked bleak for the Allies. The Germans had invaded France forcing the British to retreat at Dunkirk. Soon, the British knew, German bombers would fly across the English Channel to attack Britain from air. Even as the government struggled to evacuate people from London and build bomb shelters across the nation, the Ministry of Works had a different priority—safeguarding the invaluable art collection housed at the National Gallery at Trafalgar Square in London.

Before the war started, many paintings were already moved to various locations in Wales, including Penrhyn Castle, the university colleges of Bangor and Aberystwyth. When it became apparent that these locations were as vulnerable to bombing as London itself, a more secure location was sought. One proposal was to ship the paintings to Canada, but the risk of losing them to U-boat attacks worried the Gallery’s director Kenneth Clark. Winston Churchill too vetoed the idea and instructed Clark to a find a location within the island itself. In a telegram, he wrote to Clark: “Hide them in caves and cellars, but not one picture shall leave this island.”

The vast abandoned slate quarry in Blaenau Ffestiniog fitted the bill perfectly. The town was isolated and lonely, and the quarry itself was enormous with huge cavernous rooms. The cave’s 300 feet thick slate ceiling provided solid protection against the unlikely event of Hitler deciding to bomb this lonely mountain in north Wales.

Photo credit: Fred Ramage

Work on the quarry began immediately. The entrance to the quarry was enlarged so that trucks could drive inside allowing boxes and crates containing the paintings to be unloaded inconspicuously. Several small brick ‘bungalows’ were built within the caverns to protect the paintings from variations in humidity and temperature. To counteract the damp air in the chambers, a crude air conditioning system was devised consisting of electric fans blowing air over trays of dehydrated silica gel. The system worked so well that when the pictures went back to London, most of them were found to be in better condition than when they were at the National Gallery. This led the National Gallery to open their first air-conditioned gallery in 1949.

Throughout the period of the war, the National Gallery kept visitors entertained by holding lunchtime recitals and concerts in its now emptied building. With every concert hall in London closed, crowds flocked to the Gallery in earnest. Myra Hess, a talented but previously unknown pianist, became renowned giving concerts at the Gallery. The concerts were a huge success and won her much affection from the British public.

After the war ended and the paintings returned to the National Gallery, a small part of Manod went back into operation with a few workers, mostly producing slate slabs for industrial use. When relationship between the Soviet Union deteriorated during the Cold War, Manod was put back into standby for possible use once more.

Today, the quarry lies abandoned but the region continues to be mined supplying slate as well as granite for slabs and paving.

A large painting of King Charles I by Van Dyck barely makes it through a door. Photo credit: Fred Ramage

Paintings were moved through the caves on rail tracks. Photo credit: Fred Ramage

Photo credit: Fred Ramage

Photo credit: Fred Ramage

A painting is taken out of storage for routine inspection at the underground facility. Photo credit: Fred Ramage

Attendants take 'Cardinal Richelieu' by Philippe de Champaigne out of storage for routine inspection. Photo credit: Fred Ramage

Paintings undergoing daily dusting at Manod Quarry, north Wales. The lower painting is Rembrandt's 'Saskia as Flora'. Photo credit: Fred Ramage

Attendants take the painting 'Mother and Child', of the Botticelli school, out of storage for routine inspection in a subterranean chamber at Manod Quarry. Photo credit: Fred Ramage

Experts begin their daily undertaking of inspecting each artwork, which they did every day for almost four years. Photo credit: Fred Ramage

Ledgers with details of the artworks were also stored in the mountain hideaway. Photo credit: Fred Ramage

Mr G. Wilkinson checks the air conditioning in the caves sometime in September 1942. Photo credit: Fred Ramage

Two night security guards settle down in their subterranean dormitory. Photo credit: Fred Ramage

Chief Attendant E.B. Harrison (seated, centre) and his colleagues take a tea-break in a canteen at Manod Quarry. Photo credit: Fred Ramage