The bunker was not built from scratch. It was a former limestone quarry on land owned partly by Jesuit monks and partly by Freule Louise Poswick of Château Neercanne, and during the Second World War the Germans had already poured the concrete floors and strung the electric lighting. In April 1954, the Ministry of War leased the site for fifty years. NATO moved in the following year as 'a temporary site to be used only in war'. By Royal Decree in February 1956 it became ultra-secret, classified under the Dutch state secrets act. By 1963, with the Iron Curtain hardening, the bunker shifted to permanent twenty-four-hour occupation. In wartime, the staff would have surged to a thousand. The Belgian magazine Vox finally broke the secret in November 1980 — vaguely, as 'somewhere in the region of Maastricht.'

The complex was built to fight after a nuclear strike outside. Air pressure inside was kept slightly above atmospheric, so radiological, biological or chemical contaminants could not seep in. A decontamination shower lock guarded the entrance. The doors and access corridors were rated to resist explosion blast waves. Independent water supplies, marine diesel generators and a heating and air conditioning system held the temperature at a steady eighteen degrees Celsius year-round. Two restaurants fed the staff, the self-service capable of six hundred meals at a sitting. A hair salon kept the officers presentable. The pipes, originally insulated with cork, were re-wrapped after a smouldering fire — this time with what was then considered a wonder material. Asbestos.

In 1991, TNO researchers commissioned by the Dutch Ministry of Defence sampled the air inside Cannerberg. Flakes of blue asbestos lay on the ceilings. Three of ten air samples carried fibres above the safe limit. The dust packed into the air ducts was seriously contaminated. The conclusion was blunt: very urgent intervention required. Defence and NATO had planned to keep the bunker running until the end of 1994, but the Cold War ended faster than the asbestos problem could be ignored. Cannerberg was closed in 1992. The Alliance walked out in 1993. The men who had spent careers underground at a steady eighteen degrees emerged, many of them, into a future of slow-growing mesothelioma — the disease this kind of fibre causes thirty or forty years after exposure. The remediation took from 2003 to 2012 and cost the Dutch state forty million euros a year. Suspended ceilings were stripped, asbestos was scraped from the marl walls, and the contaminated soil thirteen metres below the floor was excavated.

The Limburg Landscape Foundation took the empty complex back in January 2012, and since September 2013 they have guided two-hour tours into the bunker for six euros a head. The artist Rob Scholte installed a work in the marl called Shelter, including a piece titled N8W8 — a sound-it-out pun on Nachtwacht, Dutch for Night Watch. The reference is local. During the Second World War, Rembrandt's Night Watch and a great number of other world-famous paintings were hidden inside the Sint-Pietersberg caves to protect them from German bombing. Scholte's embroidered version turns its back to the viewer. The Cold War operations rooms where NATO would have managed the apocalypse are now galleries. Visitors stand in Main Street and read the offices numbered low to high, the white lettering still crisp where the asbestos has been scraped away.