This could happen anywhere, but it happened to me and my mother crossing the Jura mountains between Switzerland and France about a year ago (by car).
We saw a castle on a hill above a village (sorry, can't remember the name, but like I said this could happen anywhere!). As we weren't in a hurry, we decided to make a detour and found ourselves in front of a relatively small but quite well preserved medieval castle. We parked the car on a grass verge and walked up. I would say that it was about 75 per cent intact - it had a dry moat, defensive walls, portcullis, keep, dining hall (without the roof but that was to be expected), court-yard with a well in the middle, and a few other less-defined things. We walked around for a bit, read the signs that explained the history of the place (it belonged to a local lord).
I let my imagination go free and managed to visualise men on horseback riding through the portcullis that I was looking at, with their hunting hounds. I stood in the dining hall and imagined the medieval feasts that took place there. I looked at the court-yard and and imagined the cook chasing the chickens around to make the feast, and a servant winching up a bucket of water from the well. I looked at the view from the castle down to the village and saw what they saw 800 years ago.
The second best thing of all that was that my mother and I were all alone in that castle above that tiny remote French village - no tourists, no guides. Just us and our imagination of how it must have been centuries ago.
The best thing? That was just one castle. There are many others.