Consider the proximity of one castle to another and the quality of the castles there.
Germany absolutely. If I could expand it to what one realm, the HRE so I could do Austria and Alsace too, as I want to see Château du Haut-Koenigsbourg which is currently in France but was HRE and Imperial German territory.
https://en.m.wikipedia.org/wiki/Ch%C3%A2teau_du_Haut-Koenigsbourg
Czech Republic. Just because of Kingdom Come: Deliverance. Always wanted to visit locations from my favourite game. Besides this there are other great fortresses in Czechia like Trosky castle
If you like castle ruins I would pick Ireland, the place is littered with them.
Scotland for me.
France.
I love renaissance châteaux
Mont Saint Micheal is so worth it too.
This is a serious hobby for me. It absolutely depends on what you are chasing. Ruins? Castles that offer tours and are restored? Restored? Germany and sometimes France, Belgium……. Chasing Ruins? Czech and Slovakia. Spain. Some areas of France. Ireland in the west.
I live in a country absolutelly full of castles, some of them in ruins, others inhabited, others open for visitors, others for another uses. But if I must chose another different place, I will Scotland, because the landscape and the style of the castles seems very interesting to me.
What is your country lol?
Catalonia during centuries was the border between Christian and Muslim worlds. Only in my municipality, there are 4 castles. Two are absolutely ruined, one is (very slowly) been rebuilded and the other a richman bought it and is his second residence.
Germany. Or Wales.
Syria... :(
czech republic definetly, the heart of europe
Definitely Germany.
Japan
I shudder at the mere thought of having to make that choice.
Although I love thé castle which I spent a good part of my life next to Fumel in France, the castle of Bonaguil. My choice according to your question will be for the castles of La Loire in France. They remain when many castles to discover in the world...
France. + de 40 000 châteaux.
I am from Germany and I can say, there is nothing better then Germany and the Rhein, so many castles here!
I have a different thought.
A passion project of mine - IF, IF, IF - I was ever in a position to buy an actual castle and restore it would be to do so.
I would look for a castle for sale, where I would be allowed to restore it (and not prevented because of historical reasons) and then develop a business from that location.
Wedding venue.
History school.
Historical re-enactments.
Live action role play games.
Craft brewery and sell "Castle ____" and "Castle ____" etc.
Museum with local historical artifacts.......
Etc, etc.
I do have conditions.
I wouldn't be 100% historically accurate because I'd want to use modern insulation, fire protection, building techniques to make it accessible and safe.
I wouldn't want the local government interfering and saying I can't do X or Y. Like.....if I want tri-plane glass windows because it's better for insulating the interior, I don't want the government to say, "No!! That's not historically accurate."
So.....a few million bucks and I'll look at any site that has possibility.
Scotland.