Hard to be exact as the image is not high Resolution enough i get my copy Tomorrow or Tuesday and maybe i can find more details then.
I have taken the image and applied filters etc and the image where there could be steps, does not show up as part of the image when i do this, but this just means its not a sharp detail in the image but this is due to the image itself.
So when i just zoom in and compare then i think there is a good chance its part of the Scenes you have shown, especially the last image. This looks like it could match to the Gate.
What i have noticed is at the top of this potential staircase as per last image in OT... It appears there are beings at the top of this and they seem Tiny so that shows the Scale of this place maybe?

I have used the (?) and Arrows to point to what i mean.
And so maybe yes this shot is the entrance to the Cathedral/Dome in the Images below. Which i have used a Arrow to point out the similar elements that could match below.


I have sharpened up these Images so you will have to Zoom in a bit, and indeed while its hard to make out i would say indeed the shot in the OT is the entrance to this Dome Structure.