The Valley Works in Rhydymwyn is a Government owned site that was for years so secret that it was never even shown on maps of the area.
It has now been transformed into a nature reserve and a site of historic interest, that’s now open for managed access.
The Valley Works acquired its’ name 1939 when the Ministry of Supply instructed ICI’s Special Products Division to construct a factory and storage area in the Alyn Valley close to Rhydymwyn. The factory was to manufacture mustard gas. In the years 1940-1959 it was involved in the manufacturing, assembly or storage of chemical weapons or mustard gas in bulk containers. During the years 1947-1959 the tunnel complex held the majority of the country’s stock of mustard gas.