Well upon inspection i think there is actually 2 big round doors.
What makes me say this is that the arches near the Head are bend toward the characters exploring it.
In this pic, the first arches we see bend toward the center of the room.
Soi guess that the green screen on the other side should lead to the rock tunnels the characters came from. They pass the Ampule room then find another door that leads them to the pit.
Or maybe in the leaked set photo, the arches are just not in place.