The Lapstone Zig Zag is in the Lower Blue Mountains suburb of Lapstone, west of Penrith. The 1867 Knapsack Viaduct that forms part of it is signposted from the Emu Plains exit of the Great Western Mwy (M4). From the car park at the junction to the old highway (which later used the viaduct) you can walk across. Dirt paths (only suitable for walking) descend below the massive stone arches and up to Elizabeth Lookout

The motorway uses the alignment of much of the bottom “leg” of the zig zag, but it is possible to walk from the southern end of the viaduct along the footpath next to the M4 to reach stairs to the middle leg of this engineering marvel. This uphill section is still dirt and ballast.

The top leg is more easily reached as there is a proper trailhead at the eastern end of Knapsack St, and it will take you through some of the major cuttings on smooth asphalt and past the Lucasville Station site to the upgraded Top Points Lookout, where the trains changed direction.

The 634m Lapstone Hill Tunnel, which bypassed the whole thing after only 25 years, is located mainly south of the curving Great Western Hwy (A32). A second railway viaduct (Knapsack No. 2), was completed to the east in 1913 to reach the Lapstone Hill Tunnel and is still in use in conjunction with a wider, two-track Glenbrook Tunnel. The Lapstone Hill one was closed after only 21 years but may make a comeback for cyclists and pedestrians. An upgraded track to the eastern portal of the old tunnel has already been built from Governors Drive, Lapstone, next to a water reservoir.