Reckless by Cornelia Funke

Will Reckless has followed his brother through a magic mirror into a strange fairy tale world and been slashed by a Goyl, a terrible creature made of stone whose wounds turn flesh to stone courtesy of the magic of a dark fairy.  Jacob found the mirror in his father's study and although he has never found his father in the world beyond there is plenty of evidence that he was there, iron bridges, mementoes from his world in the city museum, and the memories of people.  But the world is under threat, the troglodyte Goyl have come out from beneath the mountains under their warmaking King Kami'en and the Empress is preparing to sacrifice her daughter for the price of peace.  A spellbinding ride through the darker side of fairytales, the corpses of Sleeping Beauty's failed suitors hang from the thorns of the roses that defended her castle, trees pinion humans to have their eyes pecked out, magic is as deadly as it is glamarous.  My only niggle was the apparent lack of care of Jacob for the mother and brother he left behind, but a great imagination