Dunnottar Castle
     

I think this is my favorite Scottish castle; awesome place near Aberdeen, what else can I say? This thing sits up on its cupcake-shaped island mount right out of the North Sea and has an extremely elaborate gatehouse involving caves and tunnels and formidable gun loops, but the plateau has nice domestic buildings (however, the weather must have been horrible most days of the year). It was used as a prison camp during the 17th C religious wars and some awful things happened here.