Fablehaven

From the introduction:

Here, dozens of hidden preserves around the world shelter all the creatures of magic whose habitats have been destroyed by humanity. Fairies, goblins, centaurs, perytons, leprechauns, trolls and giants and more. All bound by treaty not to leave, or to much bother each other. So a preserve is a place of hidden beauty and wonder, but also a place with dark places even the caretakers dare not venture uninvited.