William Watkins. Its purpose was to carry the Main Western railway line across Knapsack Gully. It formed part of the Zig Zag, which climbed the eastern escarpment from Emu Plains to today's Glenbrook. Whitton also designed and built the Victoria Bridge across the Nepean River at Penrith. Construction of the Knapsack Gully Viaduct started in March 1863 by contractor W. Watkins, who also completed the stone piers of the Victoria Bridge at Penrith. Work was completed in 1865, with the bridge being constructed from local sandstone quarried in the neighbourhood around Lapstone, and carried a single rail line. The viaduct fell into disuse in 1913 after the completion of the Glenbrook Gorge Deviation. In 1926, after over a decade of disuse, the Knapsack Viaduct was taken over by the Main Roads Board. The board sought to improve the route of the Great Western Highway between Emu Plains and Blaxland, that at the time zig zagged up Mitchell's Pass which replaced Old Bathurst Road in 1832. The viaduct's carriageway was widened to allow for two car lanes, by trimming back the inside face of the stone parapets. The new road was opened by Governor Sir Dudley DeChair on 23 October 1926. The viaduct was again widened in 1939, with the construction of a reinforced concrete cantilevered deck, because of increased traffic use. The final deviation of the Great Western Highway, with the opening of the M4 Western Motorway in 1993, ended traffic flow across the Knapsack Viaduct. In 1995 the Viaduct was reopened to the public as part of the historic Lapstone Zig Zag walk. Present day The line of the old track and cuttings (including the long abandoned platform of Lucasville station), and the old Knapsack Gully bridge is now a popular bushwalking track. Often a cacophony of birdsong and insects can be heard where the gully is deep at the viaduct and it would tend to echo these sounds, especially that of the bell miner. Although the original tunnel is closed there is also a bush walk that will take you close to its entrance. Gallery See also 1892 Glenbrook Deviation 1913 Glenbrook Deviation 1892 Glenbrook Tunnel 1913 Glenbrook Tunnel Lennox Bridge, Glenbrook List of tunnels in Australia Lithgow Zig Zag Coordinates - Knapsack VIaduct - Bottom Points - Top Points - Lucasville Platform - Breakfast Point halt - Glenbrook Tunnel east portal - Glenbrook Tunnel west portal -