Neverwheeeeere.

Since you're all up in England's bidness, I very strongly suggest Neverwhere and/or anything ever by Neil Gaiman. A story about a man who goes down into the London Underground tunnels and the alternate world that waits down there.

Neverwhere is the story of Richard Mayhew and his trials and tribulations in London. At the start of the story, he is a young businessman, with a normal life. All this changes, however, when he stops to help a mysterious young girl who appears before him, bleeding and weakened, as he walks with his fiancée to dinner to meet her influential boss.