The Golden Compass by Philip Pullman
Traveling to the Arctic is a lot easier when you've got heavily armored polar bears on your side. And Lyra Belacqua, Pullman's young heroine, does have that advantage. Pullman's fantasy universe includes spirit animals, magical theology, and the enchanted instruments referenced in the titles of the trilogy. It's an explosively imaginative world, and the fact that it intersects with our own at certain nodes makes it all the more tantalizing.