It's a sad fact that historical buildings often aren't really interesting enough for use in roleplaying games. They're seldom really complicated enough until you start to get into the modern day. "Seldom," not "never," and we're definitely going to be seeing some of those exceptions on this blog.
But for right now I want to focus on something that's not actually historical, but has all the good features of history while still being simple to understand and quick to use enough for gaming. And that something is Estalia.
I do not know how to do Estalia justice. This fictional nation was the creation of the late Wyatt James, who seems to have loved castles -- he had a site about British castles which appears no longer to be up. But James had another hobby, which was painstakingly designing fictitious castles, manor houses and fortifications, complete with floorplans, elevations and histories, which he wrote up under the excellent pseudonym "Grobius Shortling." Here's just one example:
Check 'em out, download a few, and keep them in your hip pocket for a game emergency.