(Inspiration): Métro (Paris)

The "Métro" ('Chemin de Fer Métropolitain') is one of the most useful ways to go everywhere in Paris. Is less deep than the London Underground, but is very big. Have 16 lines and 214km, being the 3rd longest subway of Europe (after London and Madrid).
One of the most importants stages of the story is the maze, one world inside the kid's mind. So, the metro of Paris, like the London subway, is a perfect inspiration, because remeber me a huge maze.
And like is underground, is more like a mind maze, that is inside of the people's head.

I don't know, but I like the underground placer since I was kid. Something misterious lives there, like the fiction creatures that will live in my story.