Atrium

The Atrium is the central hub of the facility, spanning several levels and connecting multiple hallways.

Development history
The Atrium was added sometime between Beta 0.5 and Beta 0.6, when Levels 3 and 4 were added to the game. It was an high-ceiling area on Level 3 connected to staircases to and from the laboratories on Level 2 and the administrative areas on Level 3. A cafeteria was added, which was accessible via the Atrium. A turret was also located at the center of the Atrium ceiling.

In Beta 0.9, the Atrium was completely redesigned and divided into distinct levels at Level 1, 2, and 3, with a close resemblance to Vaults found in the games Fallout 3 and Fallout: New Vegas. In this redesign, the Atrium staircase was redesigned and divided, wherein the staircase to Level 3 was relocated to the east side, while the staircase to Level 1 remained at the north side.

With the labs being at the same level as the Atrium, the south side of the Atrium provided access to the Blue and Orange lab hallways. An emergency access door to and from the Orange Hallway was located at the base of the Atrium staircase to Level 3.

In Beta 0.11, the Cafeteria was relocated from Level 2 to Level 3, now being located on the former location of the Control Room. As a result, the Control Room was subsequently relocated northwest of the Atrium, with access being provided by the west side of the upper Atrium. This allowed both sides of the Atrium to be mirrored.

In the Foundation Update, the Blue and Orange lab hallways were redesigned as Sector C West and Sector C East, respectively, each with two levels of laboratories and other rooms. As a result, the Atrium was slightly raised, and the upper level was reclassified as Level 5, while the lower level was reclassified as Level 3. The Atrium ceiling was also slightly raised.

In the Recursive Update, the hallway leading to the Control Room was merged into the Sector D hallway. A disco easter egg was also added.

Level 1
The lowest level of the Atrium is a dark area with catwalks that provide access to the facility sublevel. This level of the Atrium is connected to the Geothermal Sublevel Station of the Transit System. It is currently in the process of dismantling its former reactor infrastructure.

Level 3
The middle level of the Atrium is an open area connected to the Atrium staircase for Level 2 and Level 5, the Atrium Lounge, and a janitor's closet. It also connects to a nook located in between the Atrium restrooms, providing access to Sector C West and Sector C East.

Level 5
The highest level of the Atrium on this level consists of a U-shaped hallway overlooking the Level 3 Atrium, which branches out into the Control Room, the Atrium staircase, the Security Area, the Reception Lobby, and the Cafeteria.