In 1942, the Shorts Brothers seaplane factory, which was based on the banks of the River Medway in Rochester, was expanded significantly with the digging of tunnels into the chalk cliffs behind the original buildings. During WW2, the tunnels also acted as an air-raid shelter for local residents, before being sold to the Blaw Knox Paving Company at some point after the war. In 1978, or soon after, Blaw Knox moved out of the tunnels, leaving them abandoned ever since.
The above-ground factory has since been demolished and the land redeveloped into a residential estate, but the tunnels remain...