M42 is a sub-basement of Grand Central Terminal in Midtown Manhattan, New York City. The basement contains an electrical substation that provides electricity to the terminal and helps power its tracks' third rails. The facility opened in 1918 as a steam plant; the closest electrical substation at the time was at 50th Street. In 1929, New York Central closed the 50th Street location and reconstructed the basement facility, opening it in February 1930. It fell into obscurity for several decades, until tours were held and media was written in the 21st century focusing on the space.