From Inishmore, Aran Islands.
Dún Aonghasa, or Dun Aengus, is a highly defensible prehistoric fort on a small Irish island. You can see some of the fort’s walls to the upper right. One side of the fort is a 100m cliff face, and the other sides are protected by several rings of walls.
The rocky ground of the island was very useful in mining for defenses for the fort, including the walls and also this kind of cheval de frise shown sticking up here. One would imagine its inhabitants felt as secure as possible here.