The staircase at the exit of Vatican Museum is yet another architectural splendor of The Vatican City. It is a modern addition to the museum. Built in 1932, designed by Giuseppe Momo, the staircase comprises of two different spiral staircases. One is meant for going up to exhibits and the other for exit. Tourists gather around this architectural marvel, always puzzled which angle of shot would give the complete picture. You will see them stopping at various points along the staircase to get that one perfect last shot.
The two staircases twist like a double helix formation. And it was not built based on the double helical DNA strand, because the structure of the DNA-helix, the molecule that carries genetic information from one generation to the other was discovered much later in 1953. This staircase of Vatican Museum is counted among the ten amazing staircases of the world, see others here.