Built in 1878, the Loretto Chapel is famous for its spiral “Miraculous Staircase,” whose origins remain one of America’s most enduring architectural mysteries. According to the Sisters of Loretto, a mysterious carpenter arrived after nine days of prayer to St. Joseph, constructed the staircase entirely without nails, using no central support column, and then disappeared without taking payment. Modern engineers note the staircase’s impossible geometry, load-bearing capacity, and wood species that does not appear native to the region.