Harlech Castle, Gwynedd, Wales

Harlech's castle is both an iconic affair and another of the fortifications thrown up by England's King Edward to control the Welsh. In former times, the sea lapped the cliffs above which it holds sway. The views up and down the coast from here very much explain the site of its construction: they extend far and wide, very useful if you need to subdue an area. These days, the Welsh government agency Cadw looks after the still impressive ruins of this impressive structure.