Medieval spiral staircases usually go clockwise because it put attackers at a disadvantage!
Spiral stairs in medieval times were generally made of stone and wound in a clockwise to place attacking swordsmen who were most often right-handed at a disadvantage.
The asymmetry forces the right-handed swordsman to engage the central pike and degrade his mobility compared with the defender who is facing down the stairs.
Extant 14th to 17th century examples of these stairways can be seen at Muchalls Castle, Crathes Castle and Myres Castle in Scotland. Exceptions to the rule exist, as seen in Scala of the Palazzo Contarini del Bovolo, which winds up counter-clockwise.