Stairs come in multiple form and can have their own rotation.
The stairwell is a weak standalone stone structure that can be placed independently. It has a concealed stairway that provides access from ground level to the top. Having the same height as walls, it can be part of a wall structure. However, it cannot have any attachments atop.
In Stronghold 2, the wooden platform is also available in place of a stairwell. It is a much weaker structure, however, units can scale them instantly.
Stairs are also featured in most towers and large buildings. These stairs come built-in to the structure and cannot be destroyed separately from the building.