The Train to Impossible Places - P. G. Bell

When Suzy hears a strange noise in the middle of the night, she creeps downstairs to find a train roaring through her house. But this is no ordinary train. This is the magical delivery express for the Union of Impossible Places. Whisked on board by a troll-boy, Suzy's world is turned upside down when she's asked to deliver a cursed package to a fearsome sorceress. And quite suddenly, Suzy realises the fate of the Impossible Places is in her hands... 

The first book in the bestselling Train to Impossible Places Adventures