Narrow gauge railroads are railways with a track width less than the standard gauge of 4 feet 8.5 inches. Typically, these railroads use gauges ranging from 1 foot to 3 feet. They are often built in rugged terrains where building standard gauge railroads would be more challenging and expensive. These railroads were popular in the 19th and early 20th centuries, especially in mining regions and remote areas. Notable examples include the Colorado Narrow Gauge Railroad and the Darjeeling Himalayan Railway in India. Today, many narrow gauge lines are preserved as tourist attractions or heritage railways.