The Lapstone Zig Zag was a zig zag railway built between and stations on the Main Western line of New South Wales in Australia. Constructed between 1863 and 1865 to overcome an otherwise insurmountable climb up the eastern side of the Blue Mountains, the zig zag and associated Knapsack Viaduct, a sandstone arch viaduct, were designed by John Whitton, Engineer-in-Charge of New South Wales Government Railways, and were built by William Watkins. The zig zag was listed on the Blue Mountains local government heritage register on 27 December 1991; while the adjacent Knapsack Viaduct was listed on the New South Wales Heritage Database on 2 April 1999. The Lapstone ZigZag was the world-first ZigZag constructed on any main-line railway. The ruling grade was already very steep at 1 in 33 (3%). Another of the early plans had been to build the whole line across the Blue Mountains on a completely different route through the Grose Valley with a tunnel, but this was beyond the resources of the colony of New South Wales at the time. The track included the Knapsack Viaduct and the subsequently abandoned Lucasville station, opened in 1877. The zig zag closed in 1892 when the Main Western line was diverted via the Glenbrook Deviation and subsequently sections of the line were repurposed as the Great Western Highway, and later use as a walking track. History Nineteenth century The contract to build this railway from Penrith as far as Valley Heights, which included building the Knapsack Viaduct and the Lapstone ZigZag, was awarded to William Watkins in March 1863 but was completed eighteen months behind schedule in December 1865. It opened for traffic in 1867. Once the westbound train had crossed Knapsack Viaduct, it entered the Bottom Road of the ZigZag. There were points where the Middle Road cut backwards and sharply upwards to form the middle stroke of the Z. Beyond the points, Bottom Road extended an additional to a dead-end. It was in this area that the train stopped before it reversed direction to climb Middle Road. Similarly at the junction of Middle and Top Roads, Top Road continued some distance to buffers on the edge of Knapsack Gorge. Here the train again reversed its direction to resume the journey over the Blue Mountains. Lucasville Station was completed in 1877 on the extension section of Top Road. In 1886 the line of the Top Road extension