Narrow gauge railways are rail systems with a track width less than the standard gauge of 1,435 mm (4 ft 8.5 in). They are often used in mountainous or rugged terrain where building standard gauge tracks would be more challenging and expensive. The smaller gauge allows for tighter curves and lighter construction, making them ideal for specific applications like mining or tourism. These railways can be found in various parts of the world, including the United States, India, and Switzerland. Notable examples include the Darjeeling Himalayan Railway and the Wiscasset, Waterville and Farmington Railway. Narrow gauge railways often have a unique charm and are popular among railway enthusiasts.