The Caledonian Helix

The Caledonian Helix was a railway spiral, built to allow the line to ascend alongside a flight of steps leading to the towpath of the Caledonian Canal.

Real World Equivalent
A railway spiral is a loop of track which passes over itself in order to gain height over a short horizontal distance, allowing the line to ascend steep hills. It is used as an alternative to a zig-zag (or switchback), and avoids the need for the trains to stop and reverse direction while ascending . Examples of railway spirals can be found all over the world. A well known example in the United Kingdom can be found a Dduallt on the Ffestiniog railway. The spiral was constructed as part of the railway deviation, a 2.5 mile diversionary route built between 1965 and 1978 to bypass the new Ffestiniog hydroelectric power station. It allows the railway to rise by a height of 35 feet (11 metres) and was built entirely by the railway's volunteer workforce.

In Cornwall, a railway line from the Moorswater cement terminal forms a spiral through Coombe Junction and Liskard on the Looe Valley line, joining the Cornish Main Line towards Penzance and crossing over itself at Moorswater Viaduct.

In railway modelling, spirals are often used a space-saving method on layouts with multiple levels, allowing trains to ascend or descend between them. This type of spiral will often be built in the shape of a helix.