Mountain railway

A mountain railway is a railway that operates in a mountainous region. It may operate through the mountains by following mountain valleys and through tunnels beneath mountain passes, or it may climb a mountain to provide transport to and from the summit.
Mountain railways often use narrow gauge tracks to allow for tight curves in the track and reduce tunnel size and structure gauge, also lessening the cost of construction. Where mountain railways need to climb steep gradients, they may use steep grade railway technology, or even operate as funicular railways.
Some mountain railways have been named World Heritage Sites, such as the Darjeeling Himalayan Railway.