Fantasy RPGs can tend to draw on the Medieval period for influences, but at the same time miss out slightly on the sheer oddity of that period's worldview. Even Ars Magica seems to have skimmed past this, which is a shame. Instead, for the most part, we tend to get presented with the Conan-style fantasy angle which to my mind has never been a particularly good influence. Why? Well, I've never been completely sure that it's not been conflated with the horror that is the Renaissance Festival...
Is this because of a somewhat peculiar take on the Medieval period, combined with a vibe that owes more to Hollywood films than it does to an understanding of European history and culture? Hmm. Possibly.
However, should one want to tap into the actual period one would discover that it is full of odd imagery that wouldn't look too out of place in, say, a D&D setting. For example:
This picture comes from an excellent site called Demonagerie, over at Tumblr. There's lots of demons, dragons, monsters, knights and a variety of other images and symbolism that may help to inform or flesh out your fantasy campaign. Huzzah!