The use of magic is incredibly important to the background of your fantasy world. Not only do magical locations settle your game firmly within a genre, they are precise calibrators of theme and a player’s position in a world. Nothing evokes a sense of wonder so much as having an adventure that takes you to a manor on a turtle’s back, a wizard from a forgotten world, or the strange rituals that take place within the world tree.
Magic and its uses are vital to your setting and your game. The trick lies in mixing the two kinds of magic properly to create both wonder and engagement.
This type of magic shows up in your world in forms that are clearly understandable to the players. If they get high enough level or put enough work into it, they themselves could create that dramatic stone bridge with a wall of stone spell, or held back the hordes of undead with a consecrate. Players of an RPG must feel that most things in the world are understandable or could have been done by the players themselves (speaking strictly from a 3rd edition viewpoint). This allows the players to matter, to present themselves on the stage of history and be prepared to make their marks.
You just can’t ignore the big ideas. Any fantasy world requires an occasional sense of wonder at some sheer impossibility. Once in a while, your players should see or experience magic that lies beyond the realm of the Core Rulebook, beyond the realm of the known or the safe magic. There must be places within a fantasy world that defy explanation of any kind; the places where time runs backward, or cities float via forgotten spells, or spells come alive and dance. The sense of wonder keeps people interested, sustains them as they seek the mystery or the life beyond understanding. The moment your daily memorization of spells starts to become a chore, the world needs to remind you that it is a place of fantasy.
Generally speaking, your world needs a somewhat imbalanced mix: most magic should be understandable, something grasped and hungered after by the players. Yet here and there the truly wondrous magic must reside.
-Max Porter Zasada