Rocket to the Earth’s Core
It was an ultra-scientific machine- but it plunged Mark and Margaret into the weirdest of primitive worlds… a land beneath the Earth’s surface and forgotten by time, In those dimly lit caverns, a strange and forgotten race fought a desperate battle for survival… and blind chance would decide whether their captives would be rulers or slaves. The one certain thing was that there was no way out. (originally published in 1935)