Miraculously, it was warm on Friday too, so on the way to the airport we stopped at Finchdale Priory. It's hidden by a river in what feels like the middle of nowhere in County Durham (actually, it's only a couple of miles outside Durham). Bizarrely, the site is next to what looks like a deserted MoD camp (lots of bunkers and tangled barbed wire). Must look it up and see what exactly it was.
But back to Finchdale. It's an English Heritage site, but it's free to go in and stomp about over the ruins - as long as you don't mind paying the £3 parking charge (a bit steep). There's virtually no explanation of what's what - but it's certainly an atmospheric spot.