I built this map from open data. Every point is one of 5,793 castles, fortresses, palaces and ruins across 138 countries: 2,591 castles, 1,180 fortresses, 934 palaces and 1,088 ruins. The density is the story. Europe blazes while most of the planet stays dark.
It is a curated atlas, not a complete inventory. Germany alone has an estimated 25,000 castle sites (According to some sources). A landmark makes the map when it has a real photo on Wikimedia Commons, a Wikipedia article and exact coordinates in Wikidata, balanced across countries so the map stays explorable. France leads with 351.
You can explore every one interactively at https://thecastlemap.com/ with photos, founding centuries and short stories, plus a daily Guess the Castle game. There are no ads or sign up, everything CC0 and free to download.
You must get this sort of thing a lot, but why is the palace of Westminster missing, imo it's second in impressiveness only to Buckingham palace and it's fairly world famous. https://en.wikipedia.org/wiki/Palace_of_Westminster
And the palace of Whitehall is listed as number 7 in England, but I've never heard of it, it's mostly destroyed, and what's left is not that impressive. If it's on historical value then fair enough, but still would have thought that Westminster makes the cut.
Thanks for the feedback! Honestly I think that Claude did not take Westminister on the map because it thought that it was only a parliament, not an actual palace. You are right here.
For Whitehall, I will do further verification because the fame listing comes from how famous the place is on Wikipedia. If there are no historical value and the fame comes from it being a city district, then I would have to delete it.
I will see to it later today.