 It was originally two outdoor flights of granite-clad stairs and an escalator that connected Vesey Street to the World Trade Center's Austin J. Tobin Plaza.During the September 11 attacks, the stairs served as an escape route for hundreds of evacuees from 5 World Trade Center, a 9-floor building adjacent to the 110-story towers.The staircase is now an important feature of the National September 11 Memorial & Museum.