Next to Conisbrough viaduct lays Cadeby Tunnel. The eastern portal comes out in a quarry and the portal itself was grade II listed on the 26th of November 1987 (and is pretty) and the western portal has ankle high sludge and water (to be expected as it is down a slope to get in). Both have a few tyres and shoes and stuff thrown in for good measure.
The tunnel was built in 1849 for the South Yorkshire, Doncaster and Goole Railway Company. The head engineer was Charles Bartholomew of the River Don Company. It consists of Gritstone voussoirs and rock-faced sandstone walling. Joined buttresses flank a horseshoe arch with rustication below the impost band and roll-moulded hood-mould. Roll-moulded cornice breaks forward over the buttresses; blocking course steps up at centre. The whole this is brick lined and has good airflow and is solid underfoot once you get in there.
The line was opened on 10th November 1849 and linked the Midland and Great Northern networks; after 1864 it became part of the Manchester, Sheffield and Lincolnshire railway which itself became the Great Central Railway in 1897.
One of the arches holds a small token/homage to "The Mexborough Ragger"; a local, young gypsy girl who had cut through the tunnels to sell either water and/or rags to the workers on the other side. She is said to have stepped into the central arch when a train passed but dropped what she was carrying and when she bent down to quickly grab it, she was hit by a train killing her outright. The doll left there has been there for many years and is a bloody strange site if you don't see it right at first; all that is left now is the selection of dolls legs.