The Lapstone Zig Zag was a zig zag railway built near Lapstone on the Great Western Railway of New South Wales in Australia between 1863 and 1865, to overcome an otherwise insurmountable climb up the eastern side of the Blue Mountains. The ruling grade was already very steep at 1 in 33 (3%). The original plan had been to build the whole line across the Blue Mountains on a completely different route through the Grose Valley with a 3 km long tunnel, but this was beyond the resources of the colony of New South Wales at the time.