Amy's Pendant

Her father's inventions aren't selling and her mother lost her job. If they can't find a way to pay the rent soon, her family will lose their home. At fourteen, Amy is too young for work that pays much money, but there is a slim chance she might be able to find some. She doesn't truly believe that the antique pendant her cousin gave her for her birthday is a treasure finder. Despite what her aunt thinks, it probably isn't even magical. It certainly is strange, though, and it might be valuable in its own right, if she can figure out what it is.
Her investigations of the mysterious pendant lead her to an ancient underground labyrinth where she finds marvels beyond her imagination. Even after centuries of neglect, some of the unbelievable technology here still functions. There are mysterious lights that produce no heat, doors that open by themselves, an assortment of automated animals that seem more like people than machines, and an unseen godlike intelligence, which is determined to keep Amy from escaping and revealing its existence.