Before we move on to Bordeaux, a quick overview of France.
This is a combination both the largest cities and cities you may have heard of along with some high level geographic, attraction and wine regions. And full disclosure, I scooched Corsica west a bit.
When I was planning I’d find lots of “10 Best Castles in France” and would see jaw dropping photos of Useé, Chenonceau, or Rocamadour only to find out there is a 5+ hour car ride between them. But VERY GENERALLY, if it was a pretty Disney castle or splendid Versailles estate it would be in the Loire Valley. If it’s a fortress built into the side of a mountain or giving off a walled city medieval vibe, chances are it’s by Bordeaux or South. If it’s a “France’s prettiest village” and it looks like you get there by following breadcrumbs, it’s up by Strasbourg near Germany.
If any of those strike your fancy I would search “castles” or “chateau” in “[specific region]” to save yourself some google time. And with that know that castles are fun but you’re not going to also be riding vespas and lounging on the beach because none of those are close to the Mediterranean coast without another train or car trip. I’m all about setting expectations.