I am currently reading my way through a long list of science fiction and fantasy titles. (http://www.npr.org/2011/08/07/138938145/science-fiction-and-fantasy-finalists if you are interested in the list).
When I glanced up the tunnel I got a flash, not of vestigia, but of something older, that instinct we all inherit from the evolutionary gap between coming out of the trees and inventing the big stick. From when we were just a bunch of skinny bipedal apes in a world full of apex predators. The warning that tells you that something is watching you.