This is  the spiral staircase of the Casa Contarini del Bovolo. The real name of the family was Contarini, but the ‘del Bovolo’, ‘of the snail’ was added when this famous staircase was built, thus distinguishing their family from others with the surname Contarini. The dramatic staircase was used as a setting in Orson Welles’ film Othello  of 1951.