The Coming Race is a 150 year old book and I would give it a 8.9/10. It's a lot like Journey to the Center of the Earth. A humanoid race migrated there before a cataclysm/deluge thousands of years ago. They discovered Vril technology and carry staves. If it's true then they maybe descended from the Annunaki or Atlanteans. The areas are so vast they have mountains and giant birds. Their people use mechanical wings to get around. The men are called An and the Annunaki leader is called An/Anu.
Vril - Wikipedia
The honeycombed earth reminds me of this from The Law of One:
S78/P32. In the first density wind and fire teach earth and water. The planet learns to be formed in preparation for life.