Salted away: Cheshire salt mine to store National Archives

A worker in one of the caverns of the DeepStore vaults Photograph: Graeme Robertson for The Guardian Photograph: Graeme Robertson A tunnel into the salt mine and storage vaults Photograph: Graeme Robertson for The Guardian Photograph: Graeme Robertson One of the mine tunnels Photograph: Graeme Robertson for The Guardian Photograph: Graeme Robertson Workers filing documents in the underground facility Photograph: Graeme Robertson for The Guardian Photograph: Graeme Robertson Boxes of files Photograph: Graeme Robertson for The Guardian Photograph: Graeme Robertson Walking through the underground filing sytem Photograph: Graeme Robertson for The Guardian Photograph: Graeme Robertson A safety warning at the entrance to DeepStore Photograph: Graeme Robertson for The Guardian Photograph: Graeme Robertson/Graeme Robertson for The Guardian A safety warning at the entrance to DeepStore Photograph: Graeme Robertson for The Guardian Photograph: Graeme Robertson Workers' safety equipment for use in the storage area Photograph: Graeme Robertson for The Guardian Photograph: Graeme Robertson Workers' safety equipment for use in the storage area Photograph: Graeme Robertson for The Guardian Photograph: Graeme Robertson