William Hope Hodgson 
The Night Land [EPUB ebook] 

The sun has set, leaving only the glow of lingering vulcanism to illuminate the Earth. The Last Redoubt, a massive metal pyramid under siege from unknown forces and Powers outside in the dark, has assembled the last few million of the human race. These are held back by an energy circle known as the "air clog, " which is fueled by the Earth's internal energy. For millennia, gigantic living figures─ the Watchers─ have sat in the shadows near the pyramid, waiting for the inevitable time when the Circle's strength weakens and dies. Other living entities, some of unknown origin and others that may have once been human have been sighted in the darkness beyond. As the story commences, the narrator makes mind contact with a resident of another, forgotten Redoubt and ventures out into the darkness in search of her. To leave the security of the Circle means nearly certain death or worse.