The upper level of Park Street opened as part of the Tremont Street subway – a streetcar tunnel now carrying the Green Line – in September 1897. It was built as a cut-and-cover tunnel just below the surface of Tremont Street. From 1901 to 1908, the Main Line Elevated shared the Tremont Street subway. In November 1908, the Main Line was moved to the parallel Washington Street Tunnel under Washington Street. Similarly-constructed just below street level, it included a pair of one-way stations one block southeast of Park Street. In March 1912, the Cambridge Tunnel opened from Harvard Square to Park Street Under, one level below the streetcar platforms at Park Street. The line was extended to Washington in April 1915, and to South Station Under in December 1916. The cut-and-cover tunnel was constructed with two levels from Tremont Street until halfway between Otis Street and Devonshire Street. The bottom level carried rapid transit trains, while the upper level was constructed as a fare lobby above Washington station and a potential pedestrian passageway east and west of the station. The section of upper level tunnel under Summer Street between Washington Street and Devonshire Street was used as planned as a fare lobby with entrances from Downtown Crossing department stores and as a turnstile repair area. The section between Tremont Street and Washington Street under Winter Street was leased as to adjoining businesses as storage space. In 1922 and 1927, it was proposed to be opened as a pedestrian passageway as part of expansion of Park Street station; the 1936-built expansion did not include the passageway. On March 9, 1979, the Winter Street section was opened as an inside-fare-control pedestrian passageway to ease demand on the Red Line. A ticket counter was formerly located on the mezzanine level of Downtown Crossing station under Winter Street east of Washington Street. On August 13, 2012, the MBTA combined customer services into the Downtown Crossing location as the "CharlieCard Store". When opened in 1979, only the north half of the tunnel width was open to pedestrians. In 2017-2018, both halves were renovated to create a wider, better-lit passage.
