Location Seed: Frostways.

Frostways – Google Docs

Frostways

You’ll find these high-fantasy magical highways anywhere that has both a high mana level, and a climate that averages below freezing for half the year.  To create a Frostway: first, make a road between Point A and Point B. Over it, construct a lattice of stone or brick arches spaced regularly so that they cover (with large gaps, of course) the entire road.  Then, cover the road surface itself with ice, and the lattice with either packed snow or ice blocks or whatever other form of solid water local custom favors. Then cast a particular spell.

That turns the entire structure into a Frostway: an enclosed tunnel of magically-enhanced ice that dramatically shortens the travel time between Point A and Point B (as in, one-tenth the time, even if more generic magical speed spells or whatnot are not used).  The Frostway also maintains an internal temperature of about 25 degrees Fahrenheit, regardless of the outside temperature; this is admittedly cold, but not when compared to an arctic blizzard.  If a Frostway is disrupted with people still inside of it, nothing bad happens (except that the people inside of it are now stuck somewhere on the way from Point A to Point B, of course). Fixing a breach usually does not require a re-establishment of the original spell.

The primary limitation of a Frostway is that it will eventually melt, which means that the road has to be re-enchanted every year (individual breaks in the line can be mundanely fixed easily enough, as long as the weather is below freezing).  The advantages in seasonal travel, however, are usually deemed worth the effort by any nation-state with the resources for the initial outlay. Plus, the roads can still be used in the summer, which helps to justify the price.

One last note: of course the local military is aware of the value of Frostways.  That’s why they always make it a point to have military installations at key points along the various ways.  And patrol them regularly.