Having spent way too long playing rimworld I’m pretty sure that’s a kitchen and cold storage space. The white thing on the exterior wall is the cooler, the middle room is the kitchen counter, the outer room that connects to the hall is a dining area.

The lack of doors direct from the cooler out is intentional because your people will cut through there if there’s a door and you’ll struggle to maintain temps and cleanliness, so your people are more likely to get sick.