Kneeknock Rise by Natalie Babbitt

From the moment young Egan arrives in Instep for the annual fair, he is entranced by the fable surrounding the misty peak of Kneeknock On stormy nights when the rain drives harsh and cold, an undiscovered creature raises its voice and moans. Nobody knows what it is—nobody has ever dared to try to find out and come back again. Before long, Egan is climbing the Rise to find an answer to the mystery. Kneeknock Rise is a 1971 Newbery Honor Book.