Where she fell

Teenager Eliza and her friends are going to explore a cave near their upstate New York home, but first her friends insist on dragging her to Drowner's Swamp, a bog legendary for its dangerous sinkholes, and a place which her mother has frequently warned her about; Eliza does not want to go, and when the earth opens up and swallows her she finds herself in a system of caves--and what she finds living there is strange and dangerous beyond anything the legends could conjure up.