Sydney. It is part of a notoriously steep section of the Illawarra line south of Waterfall used in the late 19th century by steam trains and bypassed by the Helensburgh deviation in 1919. The Otford tunnel is of technical significance as an important engineering work in the early construction of the Illawarra line and was also used during the second world war as part of an explosives program. Its elaborate system of venting is an important historical remnant of the problems encountered in working this tunnel. Otford railway tunnel was listed on the New South Wales State Heritage Register on 2 April 1999 having satisfied the following criteria. The place is important in demonstrating the course, or pattern, of cultural or natural history in New South Wales. The Otford tunnel is of historical significance as a major engineering work built 1888 to connect the Illawarra line to Sydney. It is part of a notoriously steep section of the Illawarra line south of Waterfall used in the late 19th century by steam trains, and bypassed by the Helensburgh deviation in 1919. The place is important in demonstrating aesthetic characteristics and/or a high degree of creative or technical achievement in New South Wales. The Otford tunnel is of technical significance as an important engineering work in the early construction of the Illawarra line. It was the longest and steepest single line tunnel to be built at the time (5,985 ' -1824m) long, with a 1 in 40 gradient). Its elaborate system of venting is an important historical remnant of the problems encountered in working this tunnel. The place has potential to yield information that will contribute to an understanding of the cultural or natural history of New South Wales. The tunnel has research potential for its ability to reveal late 19th century tunnel construction techniques, including early industrial use of concrete. The place possesses uncommon, rare or endangered aspects of the cultural or natural history of New South Wales. The tunnel is rare as a relatively intact 1888 tunnel built for the operation of steam trains on the Illawarra line through the difficult Waterfall to Clifton terrain. The place is important in demonstrating the principal characteristics of a class of cultural or natural places/environments in New South Wales. Representative of late 19th century tunnels built by Rowe & Smith for the Illawarra line from Waterfall to Clifton. See also References Bibliography Attribution