14. 18th Street Abandoned Station
18th St, also on the IRT Line, was formerly sandwiched between 14 St-Union Square and 23 St. After World War II, the Board of Transportation embarked on a platform extension program, and this allowed 14 St and 23 St to lengthen their platforms and post new entrances at 15th street and 22nd street. As a result of the close proximity, 18 St was closed down in 1948. According to Joseph Brennan of Abandoned Stations, the underground stop was often used for publicity photos because it possessed no unusual features. The sealed off station is easily visible when riding the 6 train (and 4, 5 trains if no local trains obstruct the view) between 14 St and 23 St. See a video of the abandoned station here.