Almost all settlements throughout Nibiru are contained within a certain type of structure known as Vaults. Vaults are massive, usually sphere-shaped chambers, sometimes measuring several miles of radius, that have connections to the main power lines that run from the Core. The most valuable of them also possess direct water supply and easy links to other neighboring vaults. These structures are usually classified into three categories, from Class A, B and C, depending on how big they are and on their access to life support systems and power.
The importance of vaults and of the tunnels and corridors that connect them has shaped culture and technology in Nibiru to a tremendous degree. In times of peace, machines are developed to make life as comfortable as possible within the vaults' confines.
In times of conflict, the art of war evolves to establish the ways in which vaults are besieged, tunnels are taken and positions are held, not only from human threats (such as the one posed by scavengers) but also from rogue AIs and from the strange creatures that live under the shadows of the world.
Furthermore, as Nibiru's core sectors are settled and humanity spreads, the profession of vault hunters becomes a staple throughout the station. Vault hunters roam the unknown in search for valuable, lost vaults that can be either settled or sold to the highest bidder, embarking themselves in dangerous enterprises along with technicians, soldiers and traders in search for profit and, in some cases, a new place to call home.