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In this story, it is in the far future so that it feels like a fantasy story. The protagonist is a boy named Flea with one shriveled leg. He gets dumped in a hole by his adopted family of orcs (or trolls?). He finds a cave and keeps journeying deeper into the earth. Along the way, he finds traps and puzzles that he solves, allowing him to continue. Among them, he finds a room with flying girl-like beings, which aren't afraid of him. He kills an animal there for food, and then gets in big trouble. At the end of the journey, he meets a wizard.
Any idea what this book is called, or who wrote it?