The Royal Gunpowder Mills at Waltham Abbey, a short walk north-east of Waltham Cross, was a major British munitions factory from 1665 until 1991. The complex now opens as a partly-restored heritage site occupying 175 acres of woodland — much of it now a wildlife reserve, with herds of fallow deer wandering among the surviving 18th- and 19th-century brick and timber industrial buildings.
A small museum tells the story of British gunpowder, cordite, and explosives manufacturing, with original machinery, contemporary photographs, and reconstructed labs. Land trains shuttle visitors around the larger site between the more interesting building groups; there are guided walks at weekends. The combination of grim industrial archaeology and reclaimed nature reserve makes for an unexpectedly memorable visit. Open weekends and selected weekdays from spring to autumn.