There are levels of safety in different areas. This is for all characters including foes.
Designated safe areas:
In a designated safe area AC is tripled. This is in guarded areas. Most places that rent rooms are guarded areas.
Somewhat save areas:
In a somewhat safe area AC is doubled. This is normal inside a walled town or larger city.
Normal areas:
This is most of the world. Your AC is what it adds up to.
unsafe areas:
In an unsafe area AC is cut in half.
Deathly areas:
In a deathly area AC is cut completely. Here every attack hits.