Subway systems are underground or elevated train networks that help people travel quickly within cities. They are designed to reduce traffic congestion and provide a fast way to get from one place to another. Many major cities, like New York City and London, have extensive subway systems that connect various neighborhoods and important locations. Riding the subway is usually affordable and efficient, making it a popular choice for commuters and tourists alike. Trains run on a set schedule, and stations are often located near key attractions, such as museums and shopping districts. Overall, subways play a crucial role in urban transportation.