The Marunouchi Line is a major subway line in Tokyo, Japan, operated by the Tokyo Metro. It runs in a loop, connecting key areas such as Tokyo Station, Shinjuku, and Ikebukuro. The line is known for its distinctive red color on maps and serves as a vital transportation route for commuters and tourists alike. Opened in 1954, the Marunouchi Line spans approximately 18.3 kilometers and has 28 stations. It is one of the oldest subway lines in Tokyo and plays a crucial role in the city's extensive public transportation network, facilitating easy access to various commercial and cultural districts.