I paid a visit to Castle Conwy in Wales quite a few years ago. It's the ruins of a genuine medieval castle, and the town that surrounds it. We spent an entire day there, covering every square foot.
There is not one single photo that can do this place justice, but this one is pretty good. You simply must visit this place to appreciate it in all its ancient glory.
This picture makes it look like a sand castle, but use the cars for scale.