In a future of high technology and genetic modification the Coral Kampii, like legendary mermaids, live isolated from the Above World, but when the devices that allow them to breathe underwater start to fail, thirteen-year-old Aluna and her friend Hoku go to that forbidden place to find help
Unassuming twelve-year-old Billy Hooten, who loves reading superhero comic books, suddenly learns that he has been chosen to become the next Owlboy, whose destiny it is to save the inhabitants of Monstros, a city underneath the cemetery next to Billy's house
When fifteen-year-old Ty, who has always lived on the ocean floor, joins Topside girl Gemma in the frontier's underworld to seek and stop outlaws who threaten his home, they learn that the government may pose an even greater threat
Seeking to unravel the secret of the long enmity between unicorns and delvers, Cara travels through a strange underground world to the court of the centaur king, while on Earth, Beloved and her hunters make final plans to jump to the fantasy land of Luster and drive the unicorns to extinction
When twelve-year-old Peter and his family arrive in Greenland for his father's research, he stumbles upon a secret his mother has been hiding from him all his life, and begins an adventure he never imagines possible.
When eleven-year-old Gregor and his two-year-old sister are pulled into a strange underground world, they trigger an epic battle involving men, bats, rats, cockroaches, and spiders while on a quest foretold by ancient prophecy
When eleven-year-old Juniper begins to suspect something is wrong with her mother and father, she and her friend Giles discover they have been selling their souls, pieces at a time, to a silver-tongued creature in a terrifying fairy-tale underworld.
Life becomes more interesting for Ananka Fishbein when, at the age of twelve, she discovers an underground room in the park across from her New York City apartment and meets a mysterious girl called Kiki Strike who claims that she, too, wants to explore the subterranean world.
Eleven years after the cruel Killdeer took over the Catacombs far beneath the human's Trillium City, Juniper Belancourt, assisted by Vincent and Victor Nightshade, leads a maverick band of rats to escape and establish their own city.
Kidnapped as a baby by Puddlejumpers, little people who live in a world below puddles, twelve-year-old Ernie must find courage to save the Puddlejumpers by leading them into battle against their mortal enemies, the Troggs.
Living in isolation with a robot on what appears to be an alien world populated with bizarre life forms, a twelve-year-old human girl called Eva Nine sets out on a journey to find others like her. Features "augmented reality" pages, in which readers with a webcam can access additional information about Eva Nine's world
"After the tragic death of their father, Emily and Navin move with their mother to the home of her deceased great-grandfather, but the strange house proves to be dangerous. Before long, a sinister creature lures the kids' mom through a door in the basement. Em and Navin, desperate not to lose her, follow her into an underground world inhabited by demons, robots, and talking animals. Eventually, they enlist the help of a small mechanical rabbit named Miskit. Together with Miskit, they face the most terrifying monster of all, and Em finally has the chance to save someone she loves" -- from publisher's web site
Fourteen-year-old Will Burrows lives with his parents and younger sister Rebecca in London. He has little in common with any of them, except for a passion for digging, which he shares with his father, a museum curator and doctor of archeaology.
When Will Burrows and his friend Chester embark on a quest to find Will's archaeologist father, who has inexplicably disappeared, they are led to a labyrinthine world underneath London, full of sinister inhabitants with evil intentions toward "Topsoilers" like Will and his father
While staying with distant relatives in England, Americans Rowan, Meg, Silly, and James Morgan, with their neighbors Dickie Rhys and Finn Fachan, learn that one of them must fight to the death in the Midsummer War required by the local fairies.
After learning that his presumed-dead father may still be alive, Alfonso Perplexon, now fifteen years old, takes on the dangerous task of returning to the land of Dormia to search for him. The second book of Dormia.
The adventure begins when a strange Icelander parchment is uncovered in an old bookstore and reaches a fevered pitch that never lets up as Professor Lidenbrock, his nephew Axel, and their guide, Hans, journey to the center of the earth. From the moment they reach the extinct volcano of the Mountain of Sneffels and make their treacherous descent, their chances of reaching the surface alive again become very slim, as they encounter boiling seas, serpent-like monsters, prehistoric apes and an eerie otherworld from which no man has ever escaped.
On his way to dinner with his fiancee, Richard Mayhew helps a mysterious wounded girl lying on the sidewalk. The next day, he discovers his actions have erased him from existence and he is now consigned to the underground world of London Below.
After profiting off of a small vehicle that was not built with any existing human technology, Charles Hoy decides to assemble a group of adventurers and embark on an underground quest to bring back greater discoveries. - From Novelist