[really, REALLY bad DM]
You see tracks.
Railroad racks, of course. 
[really, REALLY bad DM]
Or you can always have a wizard with punctuality issues show up at your door babbling about a ring of power…
I like the trial idea a lot, and I also like Monkey’s idea of a pregnant lady knight out for revenge. And as another possibility… the knight has a vision in a dream that she has to make the journey. If God (or a god) tells her very firmly that it’s what she’s gotta do, then she’s gonna be saddling up the next morning. Even if she’s not really up to the trip, or she’ll be riding through snowstorms, or inconveniencing/leaving in the lurch the people in her manor, or annoying various potentates along the way. It’s all good grist for the RPG mill.