Raymond Z. Gallun 
Terror Out of the Past [EPUB ebook] 

A routine aerial survey turns into an extraordinary discovery when adventurers Perry Wilcox and Dr. Roderick Murgatroyd stumble upon an ancient, buried fortress. What begins as a scientific excavation quickly escalates into a desperate struggle against an army of robotic sentinels, programmed for a war millions of years in the making. As they delve deeper, they uncover a hidden world and a technology beyond human understanding—one that could either unlock incredible power or bring total destruction. Now, with the military waging a futile battle against the mechanical colossus, Perry and his unlikely ally, reporter Lyssa Arthurs, must venture where no one has gone before to shut down the nightmare before it consumes the world.