Underground by Jean Ferris
In 1839, visitors from miles around come to Kentucky to tour Mammoth Cave. But sixteen-year-old Charlotte, the maid at Mammoth Cave Hotel, doesn't understand its appeal. As a slave, she is already trapped, and she doesn't see the point in risking being trapped underground as well. Still, she's curious when Stephen Bishop, another slave who is the cave's expert guide and chief explorer, makes some big discoveries underground, and she's interested in Stephen himself, with his quick mind and kind ways. Then Charlotte makes a discovery of her own: runaway slaves sometimes come to the hotel seeking refuge. As she helps them, she wonders if she should run away. Stephen, on the other hand, feels that he belongs with the cave and that he is free enough when he is underground. When an opportunity presents itself, Charlotte must decide whether she should stay with Stephen or risk everything for her own chance at freedom.
New York: Farrar, Straus and Giroux, 2007