Ley Lines and Shadow Roads
The land is alive with ley line magic, and some know how to harness that power for spellcasting and magical travel. The elves used the magic of ley lines to create and sustain the shadow roads (also called the fey roads), making it possible to connect a far-flung empire. When the elves retreated from the world, their roads remained, and humans and the shadow fey learned to tap into the ley lines that sustain this magic. Player characters and villains alike can use these wellsprings of power, which flow invisibly everywhere— though the most powerful ley line conjunctions are warded or guarded, used as the foundation of great fortresses or thriving cities. In Midgard, you can increase the level of magical power to unheard-of levels, without destroying the reality of the setting outside those ley line conjunctions.