Journey to the Center of the Earth is a classic 1864 science fiction novel by Jules Verne. The story involves German
professor Otto Lidenbrock who believes there are volcanic tubes going toward the centre of the Earth.
The Lost World is a novel released in 1912 by Sir Arthur Conan Doyle
Land of the Lost (1974 TV series)
The Hollow Earth theory
Are examples of this..... now I can't put my finger on it, but I've seen Hell/Nether done somewhere before.
Hollow earth could be just as inhospitable as Hell, having killer plants, tar pits, quicksand, volcanic activity, prehistoric beasts, lizard men and so-on.
Also zombie dogs could be replaced with say werewolfs or ferral, rabbid or wild dogs.
I would also like to see tortoises on the upper Earth, and maybe use thier shells as sheilds.