The Diana's Eye — Cori Nicole Smith

When she opened the music box, Martina never imagined it would lead her on a wild adventure to save a world that she never knew existed--a world that had been secretly watching hers for thousands of years.
As apocalyptic flooding becomes a global concern, twelve-year-old Martina mourns the loss of the grandfatherly previous owner of her family's ice cream shop. He left her an intricate music box that is an exact replica of the shop, which leads her and friends Heath and London through the ice cream machine and into Sheardland: an ancient sanctuary within the Earth where magical races escape the threats humans pose to their civilizations.
Mysterious happenings that interrupt the life in perfect Sheardland lead the trio on a hunt for the Diana's Eye--one of eight orbs that hold the moon in orbit--and the creatures thought to have stolen it, who were previously thought to be extinct. To save Sheardland's inhabitants from their nightmares and keep their world from flooding too, Martina and her friends must locate whoever is using the Diana's Eye in a world they barely know.
Tales of magical creatures, hidden treasures, and conflicts both ancient and new blend together to create the story of the Diana's Eye. Can Martina and her friends navigate Sheardland in time to save its ancient races . . . without use of magic?
This is the first in the series of 6 Martina Mackenzie adventures.