Did you know that stairs in castle towers should wind upwards in a clockwise direction?
This gave the advantage to right-handed swordsmen coming from above when defending the tower. Right-handed swordsmen attempting to gain access to the tower from below would have difficulty using their swords.
Here’s a good tutorial on using Blender’s array modifier and an empty to create spiral stairs. Be sure to use as little geometry as possible in constructing your stairs for use in virtual worlds. And, of course, wind your spiral stairs to rise in a clockwise direction!
Blender 3D tutorial:
How To Model A Spiral Staircase In Blender