The genre is based on and has in turn influenced the Hollow Earth theory .
Subterranean fiction is a subgenre of adventure fiction or science fiction which focuses on underground settings , sometimes at the center of the Earth or otherwise deep below the surface .
The genre is based on and has in turn influenced the Earth   theory .
Subterranean fiction is a subgenre of adventure fiction or science fiction which focuses on underground settings , sometimes at the center of the Earth or otherwise deep below the surface .