From The Heretic Knowledge Vault
The confinement vault is set up along the lines of an old-fashioned, small-scale jail, although the elves would not give the place a name so ... plebeian. There are a number of isolated cells with barred doors, reached off a central hallway. The hall is patrolled by nondescript NPC Guards (elven variety) in massive plate armor, although Meji implies that Viradior join the patrols on occasion; at least when Misa comes calling (bearing a surreptitious note from Sarine and the Amraphels), Meji just mentally lumps her in with the "blue hooded guys" who come by less frequently than the elven living tanks. The cell doors are magic-resistant, as Meji discovers when she stupidly tries to blast one of the guards, only to have the spell (Flame Volley? Force Bolt?) backfire on her. (Somehow she's remarkably un-singed by the blast.) As yet we haven't seen anyone but Meji and Ellis incarcerated in this place, but there's room for more.
All that armor and magic resistance doesn't do the guards any good, however, when Ian Samael decides that Meji needs rescuing -- as indeed she does. He disposes of the guards in a messy, yet oddly tidy, way, and rips the door off Meji's cell without breaking a magical sweat. This, of course, has repercussions...
The confinement vault may, or may not, have a connection to the Infensus Vault, another containment structure in Praenubilus Astu that seems to function as an arsenal.