The Knapsack Viaduct and Zig-Zag are in the Lower Blue Mountains suburb of Lapstone.

Knapsack Viaduct is signposted from the M4 Motorway/Great Western Highway at the Emu Plains exit. From the car park at the junction of the old highway and historic Mitchells Pass, a concrete footpath rises gently and follows the former railway and highway route to and over the viaduct. From here, dirt paths (suitable for walking only) descend below the stone arches or climb to Elizabeth lookout, upper Zig-Zag ‘roads’ and Lucasville station.

Alternatively, the Zig-Zag and other sites can be approached from the top, from the east end of Knapsack Street.

An 634 metre-long 1892 tunnel, which bypassed the Zig-Zag, is located mainly south of the Great Western Highway. The tunnel is not open at this stage but Blue Mountains City Council are working on reopening it for cyclists and pedestrians. The entrances to the tunnel can be reached by walking tracks. The eastern entrance can be reached via a tunnel beneath the M4 to Governors Drive and then a track (overgrown at times) from near a water tank. The western end can be reached from the top of Tunnel Gully on the northern side of the Great Western Highway. Once closed in 1913, the tunnel was at times used to house a mushroom farm and to store mustard gas.