Harry Harrison 
Captive Universe 

The valley was isolated in time and space, a land of barbarous science and human sacrifice.Coatlice the Dreadful stalked the night, her twin serpent heads dealing death to taboo-breakers.Citallatonac the First Priest sacrificed anyone believed to be possessed by the gods.Chimal rebelled: he wanted to escape the atavistic confines of his lost civilisation, to venture into the unknown world beyond the valley, a world of hope, and nightmare, too.