Back to the Stone Age // Seven Worlds to Conquer — Edgar Rice Burroughs

Five hundred miles beneath the surface of the Earth lies a world of eternal day and endless horizons, in which dinosaurs still roam and cavemen hunt and terrors for-gotten in the outer world still survive.

Young Wilhelm von Horst had been given up for lost. His comrades in the expedition had sailed to the surface without him, mourning the loss of their friend.

But von Horst had not died. His only companion a barbarian girl, he battles his way to safety through terrors inconceivable on the surface of the Earth.