First, a crucial distinction. "Halls of the Ancients" is not a standard Games Workshop retail publication like House of Blades or The Book of the Outcast. Instead, it is widely regarded as a comprehensive fan-compiled resource or a specific campaign supplement that focuses on the most mysterious aspect of Necromunda: the pre-Imperial ruins buried beneath Hive Primus.
These "Halls" refer to the ancient, semi-sentient structures left behind by the planet’s original human colonists (the "Ancients") before the Age of Strife. These tunnels ignore the laws of physics, shift overnight, and contain technology that the Adeptus Mechanicus would kill entire clans to possess. necromunda+halls+of+the+ancientspdf+full
The standard Necromunda campaign assumes gangs fight over territories that produce credits. Halls of the Ancients introduces a Narrative Descent Campaign. Gangs start at the "Upper Crash Site" and fight their way down to the "Core Vault." There is no territory generation—instead, gangs collect Loot Caches (Archeotech, Wild Specimens, or Scrap). First, a crucial distinction
If you locate the Necromunda Halls of the Ancients PDF full, here is exactly what you should expect to find organized by chapter. These "Halls" refer to the ancient, semi-sentient structures
Unlike a standard Dominion campaign, the Descent campaign is vertical. Gangs start at the "Threshold" (Level 1) and must fight through six layers to reach the Heart of Silence. The "Full" PDF includes the Reputation scaling for each level, something missing from many online summaries.