This level is down stairs hidden behind a secret door in the command center for the facility’s mine. When the facility was operational, the most valuable artifacts were stored here. Many of them have been drained by a disenchanter that has gotten access to the bounty of this level, but a few things are probably still intact.
The old guardian of the artifacts is still present in the magic mirrors at the end of many of the halls, ready to attack intruders when the time is right. I can’t bring myself to key this whole map, but I’d like to draw your attention to the library, reading nooks, and book repair room in the lower left corner.