Edgar Rice Burroughs 
At the Earth’s Core [PDF ebook] 

In Edgar Rice Burroughs’ At the Earth’s Core the narrator tells of his travels in the Sahara where he encounters David Innes, the pilot of an amazing vehicle and the owner of a remarkable story. It turns out his experimental "iron mole" cannot be turned off-course and it drills itself 500 miles through the earth’s crust, breaking through into an unknown interior world. 1914’s At the Earth’s Core is the first of Burroughs’ series exploring the hollow-earth land of Pellucidar, followed by the 1915 novel titled Pellucidar.