A castle - surrounded by water or perched on a crag - is among the most visually romantic of buildings. Here are uncompromising fortresses, such as those with which Edward I ringed Wales; luxurious palaces, such as Stirling or Windsor; edifaces famed in history, like Kenilworth, where Elizabeth I was feted by her favourite, Leicester, or Berkeley, where Edward II was horribly murdered; fairy-tale towers in northeast Scotland, seven storeys high and only two rooms wide; and 19th century castles built for those nourished on Sir Walter Scott and longing, like Queen Victoria at Balmoral, for more than a whiff of medieval romance...