Going Underground - Fiction for Tweens

A continuation of the purported journal of an eight-year-old adventurer, as he faces myriad strange creatures in the underground world of Subterranea.

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 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

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.

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.

In the year 241, twelve-year-old Lina trades jobs on Assignment Day to be a Messenger to run to new places in her decaying but beloved city, perhaps even to glimpse Unknown Regions

"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

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

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.