The Royal Gunpowder Mills, set in 0.7 square kms (175 acres) of parkland at Waltham Abbey, contains a complex of waterways and narrow gauge railways geared to the movement and storage of explosives, as well as twenty one buildings of major historical importance. One of three Royal Gunpowder Mills in the United Kingdom of Great Britain and Ireland (the other mills were at Ballincollig and Faversham) this is the only site to have survived virtually intact.

The Waltham Abbey Mills represent one of the first - if not the first - examples of an industrialised factory system; they were described by local historian Thomas Fuller in 1735 as 'the largest and compleatest works in Great Britain.'

The virtually intact and largely secret site was operational for more than three hundred years, concentrating on nitro-based explosives and propellants from the 1850s. After World War II it became the Explosives Research and Development Establishment; then the Propellants, Explosives and Rocket Motor Establishment Waltham Abbey; and finally the Royal Armament Research and Development Establishment Waltham Abbey. The research centre closed in 1991 and, following funding from the Government and the Heritage Lottery Fund, the majority of the original North site was sympathetically decontaminated and a heritage visitor centre created.

The site almost certainly contained the most complex and intensive use of waterborne traffic at a single British location, with a system of canals, sluices and aqueducts fed from the River Lee. Wooden barges conferred a high level of safety in an explosive atmosphere and one was deliberately sunk in a water channel to preserve its oak structure for future restoration. However, surviving elements confirm that the network of railways was as extensive as the waterways. The first railway linked the long-demolished charcoal mill and gunpowder-mixing house to the Mills, the small stores and the main canal. By 1888 the system was largely built on raised wooden platforms 1.2 m (4 ft) wide and level with the floors of the Mills, and was of 0.7 m (2 ft 3 in) gauge. The wagons and trolleys were pushed by hand - never pulled - and were turned round on small metal turntables. The rails were generally of wood faced with iron on the top and inner surfaces.

The lines were greatly extended and converted to 0.46 m (18 in) gauge by 1897, although wagons were still pushed by hand. In the process areas all-wooden rails were used to avoid risk of sparks from wheels on steel rails, although a request to use brass rails was refused because of cost. Some wooden rails survive.

In 1916, a new line was built linking the Mills on the north and south sides of Highbridge Street and which connected with the standard gauge branch from the main Liverpool Street - Cambridge line serving Enfield Royal Small Arms Factory and the Mills' coal wharf on the bank of the Lee. Exchange sidings between the two gauges were constructed next to the wharf, although coal for the powerhouses and gas works continued to be delivered by barge. With 5.6 km (3.5 miles) of heavier track to allow locomotives, this new railway was a major undertaking with three swing-bridges for barges to pass where it crossed waterways.

Steam engines could not be used because of the risk of explosion from sparks and four Ruston Proctor paraffin-powered locomotives were bought in 1917 - these weighed 4.25 tonnes and could haul nine loaded 2 tonnes bogie wagons at up to 10 kmh (6mph). However, the majority of traffic was hauled by small battery-powered electric locomotives sourced from a variety of manufacturers from 1917. Safety was paramount, particularly on the locomotive-hauled routes which ran to a strict timetable and with signals controlling the approaches to the swing-bridges.

The Royal Gunpowder Mills has been chosen as the anchor point on a new regional tourism route - ‘˜The Industrious East' celebrates the East of England's industrial heritage and forms part of the wider European Route of Industrial Heritage (ERIH). Many of the structures are Grade I Listed.