2 ft and 600 mm gauge railways in the context of "Decauville"

A narrow-gauge railway (narrow-gauge railroad in the US) is a railway with a track gauge (distance between the rails) narrower than 1,435 mm (4 ft 8+1⁄2 in) standard gauge. Most narrow-gauge railways are between 600 mm (1 ft 11+5⁄8 in) and 1,067 mm (3 ft 6 in).

Since narrow-gauge railways are usually built with tighter curves, smaller structure gauges, and lighter rails, they can be less costly to build, equip, and operate than standard- or broad-gauge railways (particularly in mountainous or difficult terrain). Lower-cost narrow-gauge railways are often used in mountainous terrain, where engineering savings can be substantial. Lower-cost narrow-gauge railways are often built to serve industries as well as sparsely populated communities where the traffic potential would not justify the cost of a standard- or broad-gauge line. Narrow-gauge railways have specialised use in mines and other environments where a small structure gauge necessitates a small loading gauge.

The Ffestiniog Railway (Welsh: Rheilffordd Ffestiniog) is a heritage railway based on 1 ft 11+1⁄2 in (597 mm) narrow-gauge, in Gwynedd, Wales. It is a major tourist attraction located mainly within the Snowdonia National Park.

The railway is about 13+1⁄2 miles (21.7 km) long and runs from the harbour at Porthmadog to the slate mining town of Blaenau Ffestiniog, travelling through forested and mountainous terrain. The line is single track throughout with four intermediate passing places. The first mile of the line out of Porthmadog runs atop an embankment called the Cob, which is the dyke of the polder known as Traeth Mawr.

A railway turntable or wheelhouse is a device for turning railway rolling stock, usually locomotives, to face a different direction. It is especially used in areas where economic considerations or a lack of sufficient space have served to weigh against the construction of a turnaround wye. Railways needed a way to turn steam locomotives around for return journeys, as their controls were often not configured for extended periods of running in reverse; also many locomotives had a lower top speed in reverse. Most diesel locomotives, however, can be operated in either direction, and are considered to have "front ends" and "rear ends" (often determined by reference to the location of the crew cab). When a diesel locomotive is operated as a single unit, the railway company often prefers, or requires, that it be run "front end" first. When operated as part of a multiple unit locomotive consist, the locomotives can be arranged so that the consist can be operated "front end first" no matter which direction the consist is pointed. Turntables were also used to turn observation cars so that their windowed lounge ends faced toward the rear of the train.

Some early turntables rapidly became too small for their purpose as longer locomotives were introduced.