From 1869 until bypassed in 1910, by the ten tunnel deviation, the Great Zig Zag near Lithgow NSW (Whitton's Wonder) was the route of the Main West Railway line. This mammoth construction was necessary for the railway to descend 470 feet into the Lithgow valley, taking almost three years to complete. The Great Zig Zag resulted in a constant grade of 1 in 42 (2.4%). After being bypassed in 1910, the rails were lifted along the middle road plus top road to Clarence. Adventurous motorists were then able to drive along those portions of the zig zag. Access to the 494m long Clarence tunnel was prohibited during WW2 when in 1944 chemical weapons were stored inside. The Main West railway line continues to occupy the bottom road of the zig zag, climbing to plunge into the ten tunnel deviation below Mount Sinai.