Mine is Roadside Picnic. I wasn't even that into the adventure part of the story... but once I hit the speech that explains the book's title, and the point of the book landed, it really stuck with me.
Every time I see a dead animal on the side of the road, or a some ants inspecting stray drops in an empty soda can, or a mouse caught in a trap, or pretty much any situation where animals are having a terrible experience due to something humans built as a minor convenience or left lying around as trash, I think "Roadside Picnic." And I imagine the point of view of the animal encountering bizarre alien artifacts they can't and could never understand, mostly encountering horrible deaths but som