These are defensive structures located above a steep cliff, often only connected to the mainland by a small neck of land, thus utilizing the topography to reduce the ramparts needed. Although their dating is problematic, most seem to date to the Iron Age.
Dunbeg Promontory Fort (An Dun Beag)
The Dingle Peninsular
The Republic of Ireland.
OS Ref (IE): V349973 - Sheet: 70