Final Fantasy IV
Vaguely Medieval Castle is probably the most common of all fantasy settings. This is the greatest Vaguely Medieval Castle music ever composed, in any genre. Even if you've never played a Final Fantasy game in your life, it is not possible to listen to this music and not immediately think of stone walls and knights and throne rooms spear-wielding infantrymen preparing to march off to battle. So for that, this track is right at the top of the list for setting the mood just so.
It's interesting that really with no further input, when you start playing Final Fantasy IV you could figure out that Baron is the most powerful nation in the world just by listening to its theme music. It might not quite rise to the level of "I'm about to cram this spear up your ass", but it's definitely at "we both know you could never get anywhere near me with that spear" level. Somehow the music works both when Baron is under dark control and when it's freed and turned back to the good.
Musically, Final Fantasy IV did the entire RPG genre a favor by showing how it's done, and setting the bar very high. There's one more FF4 track left to go on this list. It'll come up soon.