I may have been wrong about when I would encounter the mountains: I think I got my first mountain today, during the short stretch I walked to my current yeogwan. If I'm right, then it wasn't nearly as bad as I thought it was going to be. The ground went up steadily (which is why I didn't notice the contour lines), until I found myself high above the watercourse, leaving me sweaty and breathing hard, but the inflection point inevitably arrived and saved the day. The downhill walk, after all that uphill marching, was quite gratifying. One more mountain to go. I'm guessing it'll come tomorrow.
As for traffic, let's put it this way: I haven't yet felt unsafe. Things were more dangerous in America, with its roads that are far less walker- and biker-friendly.
By the way... is that a shotgun shell (or more precisely, a spent casing)? Strangely, I had a vision, before today's walk, in which I found a shotgun shell on the ground, as I have while walking along certain American roads. Finding that shell today felt a bit surreal.