Wikipedia
A mountain railway is a railway that operates in a mountain region. It may operate through the mountains, for example by following mountain valleys and tunneling beneath mountain passes. Or it may climb mountains, in order to provide transport to and from their summits.
Mountain railways often, but by no means always, use narrow gauge to allow for tight curves in the track and reduce tunnel size and structure gauge, and hence construction cost and effort. Where a mountain railway needs to climb steep gradients, it may use steep grade railway technology, or even operate as a funicular railway.
Usage examples of "mountain railway".
That there were ways up was evident from the fact that years earlier engineers had scaled these heights and erected the pylons that carried the cables of the now useless mountain railway.
There were planning Ghosts who implored them to dam the river, cut down the trees, kill the animals, build a mountain railway, smooth out the horrible grass and moss and heather with asphalt.