The pedestrian tunnel under Sixth Avenue between 34th and 40th Streets was closed to the public after a couple of murders were committed there. When the Sixth Avenue subway was built, the tracks had to be fairly deep below the street surface in order to pass under existing subway lines (42nd Street Shuttle and BMT Broadway subway). Rather than spending the money to backfill the excavation, the space was left open and the walkway built above the track level. There were intermediate stairways to the street at 36th and 38th Streets - now all sealed. It used to be possible to walk underground from Bryant Park all the way to 8th Avenue and 31st Street - I did it many times, especially on rainy days. When the subway station at 6th Avenue and 34th Street was rehabilitated a few years ago, the turnstiles/ fare controls were relocated blocking the free access route. They would have to be shifted again, at consderable expense, to creat a clear passageway outside the fare controls should the walkway up to Bryant Park be reopened.