This spiral staircase, in the Loretto Chapel in Santa Fe, has no newel, or central pole — its treads are upheld by stringers, notched structural supports as in a conventional stair, but here the stringers make two complete turns as the helical stair rises 20 feet to the choir loft. All of this is held together by wooden pegs rather than glue or nails.

It was built sometime between 1877 and 1881, but the creator’s identity is not recorded. “It’s a magnificent work of art that humbles me as a master carpenter,” wrote Tim Carter in the Washington Post in 2010. “To create a staircase like this using modern tools would be a feat. It’s mind-boggling to think about constructing such a marvel with crude hand tools, no electricity and minimal resources.”