I first played it in 1994, I think. It was a game about castles - and no, not Castles. It was like a learning/fun game, with a castle to explore, people to meet (I'm pretty sure it had some full-motion video) - you got to visit different areas of the castle, learn about things, interact with characters. I remember getting thrown in jail for snooping.
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Thanks, but no cigars yet. :-) I remember Mind Maze, but that's not it. It was definitely a stand-alone game. I think the main screen was a view of a castle, above and under ground, and you could click on different areas that would reveal areas of the castle. You even got to learn about the waste disposal system. :-)
Anyway, I appreciate the help. I'll try doing some searching this weekend.

Scooter?

I remember playing something similar to that when I was young, except it took place on some kind of pirate ship, had exploration, adventure, and puzzle elements.

I'm guessing this isn't what you are thinking of, but there was something very similar in some of the old Microsoft Encarta programs!
It was called 'Mind Maze' or something like that, but it pretty much matches your description, as you walked around a castle, talking to characters, and having to solve questions by looking them up in the encyclopedia.