See this book? It's called せんろはつづく. Or "Senro wa tsuzuku" ("The Tracks Go On And On"). It's a children's book by husband and wife team Fumiko Takeshita and Mamoru Suzuki. And it's the inspiration behind Spirit Tracks.
In one of his regular "Iwata Asks" columns, the Nintendo president sat down with Zelda mastermind Eiji Aonuma and picked his brains about the development of The Legend of Zelda: Spirit Tracks. And Aonuma revealed that the latest Zelda game was inspired not by some sweeping work of fantasy, or lasting tale of good vs evil, but by a kids book. About a train, some kids, and some animals.
In "The Tracks Go On And On" (which Aonuma was reading to his son at the time), some kids are running a train, and laying the tracks for it as they went, exploring the land. All cute stuff, with bright colours, small animals, etc. Eventually, they finish up, build a station and a real train comes. Which they promptly board, go home, end of story.
Aonuma says he kept the inspiration a secret, instead pitching the idea of exploring Hyrule on a train as though it came to him in a vision. And now, we have a Zelda game where Link travels around Hyrule on a train.
Iwata Asks [Nintendo]