Some nice folks on my tour told me about the Loretto Chapel in Sante Fe that is built in the similar cantilevered style of the famous staircase at the Nathaniel Russell House at 51 Meeting Street. The Loretto chapel was built in 1878, after Catholic nuns asked for help in building a passageway from their chapel to a choir area 22 feet above. They apparently prayed for help to St. Joseph, the patron saint of carpenters, and had their prayer answered by an anonymous builder, who fashioned the magnificent staircase to spiral upward in elliptical shape without any supporting wall.
How interesting that the 3-story staircase at the Russell house also goes up without any support, and the carpenter is also unknown. Even more intriguing is that the Russell house also became home to nuns in 1870, when the Sisters of Charity of Our lady of Mercy moved in and turned the house into a convent school.