Ancient Civilizations Challenge - 02

We've found something
Past the main gates...
A giant cylindrical structure, once sealed from the space outside, is cracked and decayed.
The structure, half buried underground, appears to have been some sort of industrial facility.
Massive sprawling refineries and buildings, half buried in sediment, fill the footprint of this cylinder-dome.
What was going on here?
The landscape ahead appears never-ending.