The Loretto staircase – built within the Loretto Chapel in New Mexico, USA – is by far the most remarkable staircase ever built. It features a double-helical spiral structure that spans 20 feet in altitude, and remains intact without the use of a central pole. The staircase is built mostly out of wood and is held together by wooden pegs and glue rather than nails or other hardware.

The staircase is venerated by Catholics as being miraculous, not due to its marvel, but based on the events that have been passed down by the Sisters of chapel ever since it was built in the late 1800s. Before the construction of the Chapel could be completed, the architect responsible for the building's design had suddenly died, leaving the nuns without access to ...