Mainly, it's probably because the entire setting—besides the tower/tunnel—is the 14-mile trail I hike out at the St. Marks Wildlife Refuge in North Florida. Which I've been hiking for over 15 years now. So basically, I know it like the back of my hand, and a lot of weird things have happened out there. I once had to jump over an alligator, seen a Florida panther out there, been charged by both otter and boar, and experienced the weirdness of seeing dolphins come into fresh water canals at high tide, since it's on the coast, in part. And gotten lost there, too.And this is the horror that inspires him:
I remember a novel by Ramsey Campbell where this guy is driving down a lonely forest road. The road loops and in the straight-aways, he sees some *thing* running down the road toward him, along the loop. So he only sees it, getting closer, on the straight-aways.