Guards need a place to rest their heads between shifts. While some might have families and be quartered elsewhere, at least a few of the unattached guards would benefit from this Barracks (Y6). The amount of time since the complex has been occupied is yet to be determined, so a more detailed description of the various contents here will need to be adjusted but at the least, four stone slabs to serve as the bases for beds and a table with four stools around it would be here. A footlocker with a padlock at the foot of each bed seems likely. It's probably a good idea to keep this sparse and with it not being secret, perhaps the locks will have been broken. This doesn't preclude a secret compartment in one or more of the footlockers.
(Cartography by Dyson Logos, modified)