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.
Read the other comments, fool. Don't just point fingers. I'm not the one that started this. You are. By commenting "Goes to show you shouldn't assume you know everything." How's that? By being curious and asking questions? Yep, that sounds like someone who thinks they know everything. Not so great when the horse bucks you off, is it? (I'm not the horse in this case; I'm just keeping with the idiom).