I've dubbed Raglan Castle as "The Accidental Castle", as I stumbed upon it by pure chance. I was actually trying to get to Monmouth Castle, which is about 6 miles to the East. That Monmouth is a total maelstrom of roads from which unwary travellers seem to get spat out in random directions, and that pretty much every road sign in Wales is half covered by vegetation, are the only reason I found it. And thank god I did! It's a mighty impressive place.
It was used as a fortress right up until the end of the English Civil War, during which it was a Royalist headquarters. When Parlementarian forces finally captured it, they razed it so it could never be used again.