The curved wall separating the interior area from the elevators and lifts, supporting the ceiling and providing the viewing surface for the videos that mimicked the day and night. These walls had large openings at the compass points with smaller doors along the circumference, allowing access to the travel corridor.
Within the habitats, it is also used as a direction point, along with "wallwards" to indicate moving away from the center, with "centerwards" or "toward the Inner Circle" being its opposite.