Bramante Staircase 1

This is probably the most photographed spiral staircase in the world.
Even though it is usually referred to as the Bramante staircase, the proper name wold be the Momo staircase.
It is designed by Giuseppe Momo in 1932, inspired by the original double helix staircase - also located in the Pio-Clementine Museum - designed in 1505 by Donato Bramante.